Don't include puresize.h any more as code that needs it

Don't include puresize.h any more as code that needs it
has moved to keyboard.c.
(menu_item_equiv_key, menu_item_enabled_p_1, menu_item_enabled_p):
Functions deleted; code moved to parse_menu_item in keyboard.c.
(single_keymap_panes): Large part of code moved to single_menu_item.
(single_menu_item): New function that uses parse_menu_item.
(Qmenu_alias): Variable deleted.
(QCtoggle, QCradio): New variables.
(syms_of_xmenu): Change initializations of variables.