enable full linter across the codebase (#9620)

enable linter using golangci-lint across
codebase to run a bunch of linters together,
we shall enable new linters as we fix more
things the codebase.

This PR fixes the first stage of this
cleanup.

pkg/dsync/drwmutex_test.go

@@ -314,7 +314,7 @@ func benchmarkRWMutex(b *testing.B, localWork, writeRatio int) {
 				rwm.Unlock()
 			} else {
 				rwm.RLock(id, source)
-				for i := 0; i != localWork; i += 1 {
+				for i := 0; i != localWork; i++ {
 					foo *= 2
 					foo /= 2
 				}

pkg/dsync/retry.go

@@ -128,13 +128,6 @@ const (
 	defaultRetryCap  = 1 * time.Second // 1 second.
 )
 
-// newRetryTimer creates a timer with exponentially increasing delays
-// until the maximum retry attempts are reached. - this function provides
-// resulting retry values to be of maximum jitter.
-func newRetryTimer(ctx context.Context, unit time.Duration, cap time.Duration) <-chan int {
-	return newRetryTimerWithJitter(ctx, unit, cap, MaxJitter)
-}
-
 // newRetryTimerSimple creates a timer with exponentially increasing delays
 // until the maximum retry attempts are reached. - this function is a
 // simpler version with all default values.