Remove find_old_style_renaming_symbol

Remove find_old_style_renaming_symbol

We found a case where a "bt" was very slow with Ada code.  Profiling
with callgrind showed this to be primarily due to calls to
find_old_style_renaming_symbol.  Because new-style renaming symbols
were implemented in 2007, it seems safe enough to remove this old
code.

A "-batch -ex bt" test on a large Ada program improves from:

    13.23user 0.57system 0:13.82elapsed 99%CPU (0avgtext+0avgdata 571408maxresident)k

to

    4.25user 0.48system 0:04.74elapsed 99%CPU (0avgtext+0avgdata 559844maxresident)k

with this patch.

Tested on x86-64 Fedora 29.  Joel reviewed this internally; and as it
is Ada-specific, I am checking it in.

gdb/ChangeLog
2019-05-28  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_remove_Xbn_suffix)
	(find_old_style_renaming_symbol)
	(parse_old_style_renaming): Remove.
	(ada_find_renaming_symbol): Don't call
	find_old_style_renaming_symbol.
	(ada_is_renaming_symbol): Rename from
	ada_find_renaming_symbol.  Remove "block" parameter.  Return
	bool.  Now static.
	(ada_read_var_value): Update and simplify.
	* ada-exp.y (write_var_or_type): Remove old code.