Remove now-unused reset_variables relying on implem details

It is used in a txt draft which I didn't change, it can be done if deemed necessary
I think this function should be kept off, as it is both more dangerous and slower than the workarounds

game/scripts/utility/common_functions.rpy

@@ -102,20 +102,6 @@ init python early:
             print("Error evaluating data:")
             print(e)
 
-    def reset_variables(*args):
-        """Resets the given variables to their default values."""
-        # Refer to renpy.ast.Default.set_default for implementation details
-        defaults_set = renpy.store._defaults_set
-        changed_set = renpy.store.__dict__.ever_been_changed
-        for arg in args:
-            if arg in defaults_set:
-                if arg in changed_set:
-                    defaults_set.remove(arg)
-                    changed_set.remove(arg)
-            elif config.developer:
-                raise Exception("The variable `{}` was not previously set with a default value.".format(arg))
-        renpy.execute_default_statement(False)
-
     def disable_game_menu():
         setattr(renpy.store, "_game_menu_screen", None)