Use bool for boolean in xmenu.c, xml.c

Use bool for boolean in xmenu.c, xml.c

* xmenu.c (x_menu_set_in_use, popup_get_selection)
(Fx_menu_bar_open_internal, popup_widget_loop)
(x_activate_menubar, xg_crazy_callback_abort)
(update_frame_menubar, set_frame_menubar)
(initialize_frame_menubar, free_frame_menubar)
(create_and_show_popup_menu, x_menu_show)
(create_and_show_dialog, x_dialog_show):
* xml.c (libxml2_loaded_p, init_libxml2_functions, parse_region)
(Flibxml_parse_html_region, Flibxml_parse_xml_region):
* xrdb.c (main) [TESTRM]:
* xsettings.c (init_gsettings):
* xterm.c (XFillRectangle, xg_scroll_callback)
(xg_end_scroll_callback):
* xterm.h (x_menu_set_in_use) [USE_GTK || USE_MOTIF]:
Use bool for boolean.
* xmenu.c (TRUE): Remove; no longer used.
(show_help_event): Remove long-unused code.
(set_frame_menubar): Remove "#if 1" and corresponding "#endif" lines.