Move event_object_movement_helpers into event_object_movement

ld_script.txt

@@ -93,7 +93,6 @@ SECTIONS {
         src/field_door.o(.text);
         asm/field_player_avatar.o(.text);
         src/event_object_movement.o(.text);
-        src/event_object_movement_helpers.o(.text);
         src/field_message_box.o(.text);
         src/map_obj_lock.o(.text);
         src/text_window.o(.text);