add gocritic/ruleguard checks back again, cleanup code. (#13665)

- remove some duplicated code
- reported a bug, separately fixed in #13664
- using strings.ReplaceAll() when needed
- using filepath.ToSlash() use when needed
- remove all non-Go style comments from the codebase

Co-authored-by: Aditya Manthramurthy <donatello@users.noreply.github.com>

cmd/bucket-targets.go

@@ -444,6 +444,6 @@ type TargetClient struct {
 	StorageClass        string // storage class on remote
 	disableProxy        bool
 	healthCancelFn      context.CancelFunc // cancellation function for client healthcheck
-	ARN                 string             //ARN to uniquely identify remote target
+	ARN                 string             // ARN to uniquely identify remote target
 	ResetID             string
 }