Remove now-unused Ada evaluator code

Remove now-unused Ada evaluator code

Now that the Ada parser has switched to the new style, there is no
need for the old Ada evaluation code.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* ada-lang.c (resolve_subexp, replace_operator_with_call)
	(evaluate_subexp_type, assign_aggregate)
	(aggregate_assign_positional, aggregate_assign_from_choices)
	(aggregate_assign_others, ada_evaluate_subexp_for_cast)
	(ada_evaluate_subexp, ADA_OPERATORS, ada_operator_length)
	(ada_operator_check, ada_forward_operator_length)
	(ada_dump_subexp_body, ada_print_subexp, ada_exp_descriptor):
	Remove.
	(post_parser): Update.
	(class ada_language) <expresssion_ops>: Remove.