Remove the last setattr on the store

benign in this case since the variable is builtin, but consistency and good practices

(cherry picked from commit 1d1d18ad1c)

game/scripts/utility/common_functions.rpy

@@ -119,10 +119,12 @@ init python early:
         renpy.execute_default_statement(False)
 
     def disable_game_menu():
-        setattr(renpy.store, "_game_menu_screen", None)
+        global _game_menu_screen
+        _game_menu_screen = None
 
     def enable_game_menu():
-        setattr(renpy.store, "_game_menu_screen", "save_screen")
+        global _game_menu_screen
+        _game_menu_screen = "save_screen"
 
     def make_revertable(obj):
         if isinstance(obj, _list):