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>

internal/crypto/sse-s3.go

@@ -80,7 +80,7 @@ func (s3 sses3) UnsealObjectKey(KMS kms.KMS, metadata map[string]string, bucket,
 	if err != nil {
 		return key, err
 	}
-	err = key.Unseal(unsealKey[:], sealedKey, s3.String(), bucket, object)
+	err = key.Unseal(unsealKey, sealedKey, s3.String(), bucket, object)
 	return key, err
 }