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/bucket/object/lock/lock.go

@@ -193,6 +193,7 @@ func (dr *DefaultRetention) UnmarshalXML(d *xml.Decoder, start xml.StartElement)
 		return fmt.Errorf("either Days or Years must be specified, not both")
 	}
 
+	//nolint:gocritic
 	if retention.Days != nil {
 		if *retention.Days == 0 {
 			return fmt.Errorf("Default retention period must be a positive integer value for 'Days'")