Remove dead code.

Remove dead code.

	* libmisc/find_new_sub_gids.c: Remove dead code.
	find_new_sub_gids() is always called with *range_count set to 0.
	It's more difficult to keep the subordinate GIDs and UIDs
	synchronized, than for the user's UID/GId because the count of
	subordinate IDs may differ.
	* libmisc/find_new_sub_uids.c: Likewise.
	* lib/subordinateio.h, lib/subordinateio.c: Remove APIs that are
	no more needed: is_sub_uid_range_free(), is_sub_gid_range_free(),
	is_range_free().