hash, mgetgroups: drop xalloc dependency

hash, mgetgroups: drop xalloc dependency

Rely on the new xalloc-oversized module to avoid requiring
xalloc-die for functions documented as returning NULL on
potential allocation overflow.

* lib/hash.c (includes): Adjust includes.
* lib/mgetgroups.c (includes): Likewise.
(xgetgroups): Move...
* lib/xgetgroups.c: ...to new file.
* modules/xgetgroups: New file, split from...
* modules/mgetgroups: ...here.
(Depends-on): Add xalloc-oversized.
* modules/hash (Depends-on): Likewise.
* modules/hash-tests (Depends-on): Drop xalloc.
(test_hash_LDADD): Drop unused library.
* tests/test-hash.c (main): Break xalloc dependency.
(includes): Drop unused include.

Signed-off-by: Eric Blake <eblake@redhat.com>