Remove unnecessary/incorrect talloc_steal() calls

Remove unnecessary/incorrect talloc_steal() calls

The talloc_steal() in dsdb_enum_group_mem() is unnecessary, because
members was already allocated from the same mem_ctx.

The talloc_steal() in pdb_samba_dsdb_enum_aliasmem() is also unnecessary
for the same reason, but also incorrect, because it should be
dereferencing pmembers:

    talloc_steal(mem_ctx, *pmembers);

Furthermore, we should only assign to *pnum_members on success; otherwise
num_members is used uninitialized.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14264

Signed-off-by: Jonathon Reinhart <Jonathon.Reinhart@gmail.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Thu Mar  5 18:40:16 UTC 2020 on sn-devel-184