Avoid needless casts with XSAVE_POINTER.

Avoid needless casts with XSAVE_POINTER.

* alloc.c (mark_object) [GC_MARK_STACK]:
* dired.c (directory_files_internal_unwind):
* fileio.c (do_auto_save_unwind):
* gtkutil.c (pop_down_dialog):
* keymap.c (map_keymap_char_table_item):
* lread.c (load_unwind):
* nsmenu.m (pop_down_menu):
* print.c (print_object) [GC_MARK_STACK]:
* xfns.c (clean_up_file_dialog):
* xmenu.c (cleanup_widget_value_tree):
Omit casts between XSAVE_POINTER and a pointer type.