trylock: Use sync.Mutex in go1.18+

Go 1.18 supplements Mutex with a TryLock method.
Use this directly instead of our dumb homebrew
trylock mutex when Go 1.18 is in use.

.github/workflows/build.yml

@@ -24,7 +24,7 @@ jobs:
       working-directory: ./cmd/dcrdata
 
     - name: Install Linters
-      run: "curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.48.0"
+      run: "curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.50.1"
 
     - name: Go Tests
       env:

trylock/trylock.go

@@ -1,6 +1,9 @@
-// Copyright (c) 2021, The Decred developers
+// Copyright (c) 2021-2022, The Decred developers
 // See LICENSE for details.
 
+//go:build !go1.18
+// +build !go1.18
+
 package trylock
 
 import (
@@ -11,7 +14,8 @@ import (
 
 // Mutex is a "try lock" for coordinating multiple accessors, while allowing
 // only a single updater. It is not very smart about queueing when there are
-// multiple callers of Lock waiting.
+// multiple callers of Lock waiting. DEPRECATED: sync.Mutex has TryLock
+// functionality built-in as of Go 1.18.
 type Mutex struct {
 	mtx sync.Mutex
 	c   chan struct{}

trylock/trylock_go1.18.go

@@ -0,0 +1,13 @@
+// Copyright (c) 2022, The Decred developers
+// See LICENSE for details.
+
+//go:build go1.18
+// +build go1.18
+
+package trylock
+
+import "sync"
+
+// Mutex is just an alias for sync.Mutex in Go 1.18 onward since TryLock() was
+// added to the standard library.
+type Mutex = sync.Mutex