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/storage-rest_test.go

@@ -29,13 +29,8 @@ import (
 	xnet "github.com/minio/pkg/net"
 )
 
-///////////////////////////////////////////////////////////////////////////////
-//
 // Storage REST server, storageRESTReceiver and StorageRESTClient are
 // inter-dependent, below test functions are sufficient to test all of them.
-//
-///////////////////////////////////////////////////////////////////////////////
-
 func testStorageAPIDiskInfo(t *testing.T, storage StorageAPI) {
 	testCases := []struct {
 		expectErr bool