startupmigrations: remove no-op SET CLUSTER SETTING version

The migration writing the initial value of the cluster version setting
was also performing a `SET CLUSTER SETTING version = v`, where v was the
version is had just written in the settings table. This statement was a
no-op, because it amounted to an update from v to v [1].
This patch removes the statement.

[1] https://github.com/cockroachdb/cockroach/blob/f87728fee6d16e2a352ac76e7ae9225930032ce6/pkg/upgrade/upgrademanager/manager.go#L167-L171

Release note: None
Epic: None

pkg/server/admin_test.go

@@ -1055,10 +1055,10 @@ func TestAdminAPIEvents(t *testing.T) {
 		{"create_database", false, 0, false, 3},
 		{"drop_table", false, 0, false, 2},
 		{"create_table", false, 0, false, 3},
-		{"set_cluster_setting", false, 0, false, 4},
+		{"set_cluster_setting", false, 0, false, 3},
 		// We use limit=true with no limit here because otherwise the
 		// expCount will mess up the expected total count below.
-		{"set_cluster_setting", true, 0, true, 4},
+		{"set_cluster_setting", true, 0, true, 3},
 		{"create_table", true, 0, false, 3},
 		{"create_table", true, -1, false, 3},
 		{"create_table", true, 2, false, 2},

pkg/startupmigrations/migrations.go

@@ -770,28 +770,6 @@ func populateVersionSetting(ctx context.Context, r runner) error {
 		}
 	}
 
-	// NB: We have to run with retry here due to the following "race" condition:
-	// - We're attempting to the set the cluster version at startup.
-	// - Setting the cluster version requires all nodes to be up and running, in
-	//   order to push out all relevant version gates.
-	// - This list of "all nodes" is gathered by looking at all the liveness
-	//   records in KV.
-	// - When starting a multi-node cluster all at once, nodes other than the
-	//   one being bootstrapped join the cluster using the join RPC.
-	// - The join RPC results in the creation of a liveness record for the
-	//   joining node, except it starts off in an expired state (leaving it to
-	//   the joining node to heartbeat it for the very first time).
-	//
-	// Attempting to set the cluster version at startup, while there also may be
-	// other nodes trying to join, could then result in failures where the
-	// migration infrastructure find expired liveness records and gives up. To
-	// that end we'll simply retry, expecting the joining nodes to "come live"
-	// before long.
-	if err := r.execAsRootWithRetry(
-		ctx, "set-setting", "SET CLUSTER SETTING version = $1", v.String(),
-	); err != nil {
-		return err
-	}
 	return nil
 }