Reorganize file util functionality (#7848)

* reorganize file util functionality

* fix api test compilation

* fix rebase issue

einterfaces/emoji.go

@@ -10,13 +10,3 @@ import (
 type EmojiInterface interface {
 	CanUserCreateEmoji(string, []*model.TeamMember) bool
 }
-
-var theEmojiInterface EmojiInterface
-
-func RegisterEmojiInterface(newInterface EmojiInterface) {
-	theEmojiInterface = newInterface
-}
-
-func GetEmojiInterface() EmojiInterface {
-	return theEmojiInterface
-}