Remove bt-load.c

Remove bt-load.c

bt-load.c has AFAIK been dead code since the removal of the SH5 port
in 2016.  I have a patch series that would need to update the liveness
tracking in a nontrivial way, so it seemed better to remove the pass
rather than install an untested and probably bogus change.

2019-09-09  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* Makefile.in (OBJS): Remove bt-load.o.
	* doc/invoke.texi (fbranch-target-load-optimize): Delete.
	(fbranch-target-load-optimize2, fbtr-bb-exclusive): Likewise.
	* common.opt (fbranch-target-load-optimize): Mark as Ignore and
	document that the option no longer does anything.
	(fbranch-target-load-optimize2, fbtr-bb-exclusive): Likewise.
	* target.def (branch_target_register_class): Delete.
	(branch_target_register_callee_saved): Likewise.
	* doc/tm.texi.in (TARGET_BRANCH_TARGET_REGISTER_CLASS): Likewise.
	(TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED): Likewise.
	* doc/tm.texi: Regenerate.
	* tree-pass.h (make_pass_branch_target_load_optimize1): Delete.
	(make_pass_branch_target_load_optimize2): Likewise.
	* passes.def (pass_branch_target_load_optimize1): Likewise.
	(pass_branch_target_load_optimize2): Likewise.
	* targhooks.h (default_branch_target_register_class): Likewise.
	* targhooks.c (default_branch_target_register_class): Likewise.
	* opt-suggestions.c (test_completion_valid_options): Remove
	-fbtr-bb-exclusive from the list of test options.
	* bt-load.c: Remove.

From-SVN: r275521