target: Remove unused code

target/file.go

@@ -56,10 +56,6 @@ func (fs *Filesystem) Translate(src string) (dest string, err error) {
 	return filepath.Join(fs.PublishDir, filepath.FromSlash(src)), nil
 }
 
-func (fs *Filesystem) extension(ext string) string {
-	return ext
-}
-
 func filename(f string) string {
 	ext := filepath.Ext(f)
 	if ext == "" {