c++: Avoid unnecessary deprecated warnings.

c++: Avoid unnecessary deprecated warnings.

There's no need to warn that a deprecated function uses a deprecated type,
that just adds noise.  We were preventing that in start_decl, but that
didn't help member declarations that go through grokfield.  So handle it in
grokdeclarator instead, which is shared between them.

gcc/cp/ChangeLog
2020-05-11  Jason Merrill  <jason@redhat.com>

	* decl.c (grokdeclarator): Adjust deprecated_state here.
	(start_decl): Not here.