Remove some uses of "object_files"

Remove some uses of "object_files"

The "object_files" macro is sometimes used when iterating over
objfiles.  This patch removes a few such uses in favor of the new
range adapter.

gdb/ChangeLog
2019-04-10  Tom Tromey  <tom@tromey.com>

	* ia64-tdep.c (ia64_get_dyn_info_list): Use foreach.
	* minsyms.c (lookup_minimal_symbol): Use foreach.
	(lookup_minimal_symbol_text, lookup_minimal_symbol_by_pc_name)
	(lookup_minimal_symbol_solib_trampoline): Likewise.
	* symfile.c (reread_symbols): Use foreach.