Remove a racy test

This test is super racy, and we already have test coverage for this
functionality in the agent/cache package with TestCacheThrottle.

Instead of spending time rewriting this test, let's remove it.

```
WARNING: DATA RACE
Read at 0x00c01de410fc by goroutine 735:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:1024 +0x9af
  github.com/hashicorp/consul/testrpc.WaitForTestAgent()
      /home/daniel/pers/code/consul/testrpc/wait.go:99 +0x209
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:966 +0x1ad
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202

Previous write at 0x00c01de410fc by goroutine 605:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1.2()
      /home/daniel/pers/code/consul/agent/agent_test.go:998 +0xe9

Goroutine 735 (running) created at:
  testing.(*T).Run()
      /usr/lib/go/src/testing/testing.go:1238 +0x5d7
  github.com/hashicorp/consul/agent.TestCacheRateLimit()
      /home/daniel/pers/code/consul/agent/agent_test.go:961 +0x375
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202

Goroutine 605 (finished) created at:
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:1022 +0x91e
  github.com/hashicorp/consul/testrpc.WaitForTestAgent()
      /home/daniel/pers/code/consul/testrpc/wait.go:99 +0x209
  github.com/hashicorp/consul/agent.TestCacheRateLimit.func1()
      /home/daniel/pers/code/consul/agent/agent_test.go:966 +0x1ad
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:1193 +0x202
```

agent/agent_test.go

@@ -30,7 +30,6 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sync/errgroup"
-	"golang.org/x/time/rate"
 	"google.golang.org/grpc"
 	"gopkg.in/square/go-jose.v2/jwt"
 
@@ -937,110 +936,6 @@ func testAgent_AddServiceNoRemoteExec(t *testing.T, extraHCL string) {
 	}
 }
 
-func TestCacheRateLimit(t *testing.T) {
-	if testing.Short() {
-		t.Skip("too slow for testing.Short")
-	}
-
-	t.Parallel()
-	tests := []struct {
-		// count := number of updates performed (1 every 10ms)
-		count int
-		// rateLimit rate limiting of cache
-		rateLimit float64
-		// Minimum number of updates to see from a cache perspective
-		// We add a value with tolerance to work even on a loaded CI
-		minUpdates int
-	}{
-		// 250 => we have a test running for at least 2.5s
-		{250, 0.5, 1},
-		{250, 1, 1},
-		{300, 2, 2},
-	}
-	for _, currentTest := range tests {
-		t.Run(fmt.Sprintf("rate_limit_at_%v", currentTest.rateLimit), func(t *testing.T) {
-			tt := currentTest
-			t.Parallel()
-			a := NewTestAgent(t, "cache = { entry_fetch_rate = 1, entry_fetch_max_burst = 100 }")
-			defer a.Shutdown()
-			testrpc.WaitForTestAgent(t, a.RPC, "dc1")
-
-			cfg := a.config
-			require.Equal(t, rate.Limit(1), a.config.Cache.EntryFetchRate)
-			require.Equal(t, 100, a.config.Cache.EntryFetchMaxBurst)
-			cfg.Cache.EntryFetchRate = rate.Limit(tt.rateLimit)
-			cfg.Cache.EntryFetchMaxBurst = 1
-			a.reloadConfigInternal(cfg)
-			require.Equal(t, rate.Limit(tt.rateLimit), a.config.Cache.EntryFetchRate)
-			require.Equal(t, 1, a.config.Cache.EntryFetchMaxBurst)
-			var wg sync.WaitGroup
-			stillProcessing := true
-
-			injectService := func(i int) {
-				srv := &structs.NodeService{
-					Service: "redis",
-					ID:      "redis",
-					Port:    1024 + i,
-					Address: fmt.Sprintf("10.0.1.%d", i%255),
-				}
-
-				err := a.addServiceFromSource(srv, []*structs.CheckType{}, false, "", ConfigSourceRemote)
-				require.Nil(t, err)
-			}
-
-			runUpdates := func() {
-				wg.Add(tt.count)
-				for i := 0; i < tt.count; i++ {
-					time.Sleep(10 * time.Millisecond)
-					injectService(i)
-					wg.Done()
-				}
-				stillProcessing = false
-			}
-
-			getIndex := func(t *testing.T, oldIndex int) int {
-				req, err := http.NewRequest("GET", fmt.Sprintf("/v1/health/service/redis?cached&wait=5s&index=%d", oldIndex), nil)
-				require.NoError(t, err)
-
-				resp := httptest.NewRecorder()
-				a.srv.handler(false).ServeHTTP(resp, req)
-				// Key doesn't actually exist so we should get 404
-				if got, want := resp.Code, http.StatusOK; got != want {
-					t.Fatalf("bad response code got %d want %d", got, want)
-				}
-				index, err := strconv.Atoi(resp.Header().Get("X-Consul-Index"))
-				require.NoError(t, err)
-				return index
-			}
-
-			{
-				start := time.Now()
-				injectService(0)
-				// Get the first index
-				index := getIndex(t, 0)
-				require.Greater(t, index, 2)
-				go runUpdates()
-				numberOfUpdates := 0
-				for stillProcessing {
-					oldIndex := index
-					index = getIndex(t, oldIndex)
-					require.GreaterOrEqual(t, index, oldIndex, "index must be increasing only")
-					numberOfUpdates++
-				}
-				elapsed := time.Since(start)
-				qps := float64(time.Second) * float64(numberOfUpdates) / float64(elapsed)
-				summary := fmt.Sprintf("received %v updates in %v aka %f qps, target max was: %f qps", numberOfUpdates, elapsed, qps, tt.rateLimit)
-
-				// We must never go beyond the limit, we give 10% margin to avoid having values like 1.05 instead of 1 due to precision of clock
-				require.LessOrEqual(t, qps, 1.1*tt.rateLimit, fmt.Sprintf("it should never get more requests than ratelimit, had: %s", summary))
-				// We must have at least being notified a few times
-				require.GreaterOrEqual(t, numberOfUpdates, tt.minUpdates, fmt.Sprintf("It should have received a minimum of %d updates, had: %s", tt.minUpdates, summary))
-			}
-			wg.Wait()
-		})
-	}
-}
-
 func TestAddServiceIPv4TaggedDefault(t *testing.T) {
 	if testing.Short() {
 		t.Skip("too slow for testing.Short")