Remove is_gimple_condexpr

This removes is_gimple_condexpr, note the vectorizer via patterns
still creates COND_EXPRs with embedded GENERIC conditions and has
a reference to the function in comments.  Otherwise is_gimple_condexpr
is now equal to is_gimple_val.

2022-05-16  Richard Biener  <rguenther@suse.de>

	* gimple-expr.cc (is_gimple_condexpr): Remove.
	* gimple-expr.h (is_gimple_condexpr): Likewise.
	* gimplify.cc (gimplify_expr): Remove is_gimple_condexpr usage.
	* tree-if-conv.cc (set_bb_predicate): Likewie.
	(add_to_predicate_list): Likewise.
	(gen_phi_arg_condition): Likewise.
	(predicate_scalar_phi): Likewise.
	(predicate_statements): Likewise.