Remove bound_name static from ada-lang.c

Remove bound_name static from ada-lang.c

ada-lang.c has a "bound_name" static that is used when finding fields
in a structure in some cases.  This patch removes it in favor of
computing the desired field name at runtime; this avoids an artificial
limit.

I'm checking this in.  Tested on x86-64 Fedora 30, and also on the
internal AdaCore test suite.

gdb/ChangeLog
2020-05-20  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (bound_name, MAX_ADA_DIMENS): Remove.
        (desc_one_bound, desc_index_type): Compute field name.