gdb: remove callback in macro expand functions

I started to look into changing the callbacks in macroexp.h to use
gdb::function_view.  However, I noticed that the passed lookup function
was always `standard_macro_lookup`, which looks up a macro in a
`macro_scope` object.  Since that doesn't look like a very useful
abstraction, it would be simpler to just pass the scope around and have
the various functions call standard_macro_lookup themselves.  This is
what this patch does.

gdb/ChangeLog:

	* macroexp.h (macro_lookup_ftype): Remove.
	(macro_expand, macro_expand_once, macro_expand_next): Remove
	lookup function parameters, add scope parameter.
	* macroexp.c (scan, substitute_args, expand, maybe_expand,
	macro_expand, macro_expand_once, macro_expand_next): Likewise.
	* macroscope.h (standard_macro_lookup): Change parameter type
	to macro_scope.
	* macroscope.c (standard_macro_lookup): Likewise.
	* c-exp.y (lex_one_token): Update.
	* macrocmd.c (macro_expand_command): Likewise.
	(macro_expand_once_command): Likewise.

Change-Id: Id2431b1489359e1b0274dc2b81e5ea5d225d730c