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/gateway/azure/gateway-azure.go

@@ -274,7 +274,7 @@ func s3MetaToAzureProperties(ctx context.Context, s3Metadata map[string]string)
 	encodeKey := func(key string) string {
 		tokens := strings.Split(key, "_")
 		for i := range tokens {
-			tokens[i] = strings.Replace(tokens[i], "-", "_", -1)
+			tokens[i] = strings.ReplaceAll(tokens[i], "-", "_")
 		}
 		return strings.Join(tokens, "__")
 	}
@@ -367,7 +367,7 @@ func azurePropertiesToS3Meta(meta azblob.Metadata, props azblob.BlobHTTPHeaders,
 	decodeKey := func(key string) string {
 		tokens := strings.Split(key, "__")
 		for i := range tokens {
-			tokens[i] = strings.Replace(tokens[i], "_", "-", -1)
+			tokens[i] = strings.ReplaceAll(tokens[i], "_", "-")
 		}
 		return strings.Join(tokens, "_")
 	}

cmd/gateway/gcs/gateway-gcs.go

@@ -531,7 +531,7 @@ func toGCSPageToken(name string) string {
 		byte(length & 0xFF),
 	}
 
-	length = length >> 7
+	length >>= 7
 	if length > 0 {
 		b = append(b, byte(length&0xFF))
 	}

cmd/gateway/s3/gateway-s3-sse.go

@@ -668,7 +668,7 @@ func (l *s3EncObjects) CompleteMultipartUpload(ctx context.Context, bucket, obje
 		return oi, e
 	}
 
-	//delete any unencrypted version of object that might be on the backend
+	// delete any unencrypted version of object that might be on the backend
 	defer l.s3Objects.DeleteObject(ctx, bucket, object, opts)
 
 	// Save the final object size and modtime.