Back out earlier Ada exception change

Back out earlier Ada exception change

commit 2ff0a9473 (Fix "catch exception" with dynamic linking) changed
how ada-lang.c creates expressions to determine if an exception
catchpoint should stop.

That patch is no longer needed now that copy relocations are handled
more directly.

gdb/ChangeLog
2019-10-02  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_lookup_simple_minsyms): Remove.
	(create_excep_cond_exprs): Simplify exception string computation.
	(ada_exception_catchpoint_cond_string): Likewise.