calls.c: Remove some dead code and target hooks

calls.c: Remove some dead code and target hooks

Looking at calls.c:initialize_argument_information, I spotted some dead
code that seems to have been left behind from when MPX support was
removed.

This change removes that code as well as the associated target hooks
(which appear to be unused).

gcc/ChangeLog:

	* calls.c (initialize_argument_information): Remove some dead
	code, remove handling for function_arg returning const_int.
	* doc/tm.texi: Delete documentation for unused target hooks.
	* doc/tm.texi.in: Likewise.
	* target.def (load_bounds_for_arg): Delete.
	(store_bounds_for_arg): Delete.
	(load_returned_bounds): Delete.
	(store_returned_bounds): Delete.
	* targhooks.c (default_load_bounds_for_arg): Delete.
	(default_store_bounds_for_arg): Delete.
	(default_load_returned_bounds): Delete.
	(default_store_returned_bounds): Delete.
	* targhooks.h (default_load_bounds_for_arg): Delete.
	(default_store_bounds_for_arg): Delete.
	(default_load_returned_bounds): Delete.
	(default_store_returned_bounds): Delete.