Revert "s3:auth make sure the primary group sid is usable"

Revert "s3:auth make sure the primary group sid is usable"

This reverts commit 00089fd74af740f832573d904312854e494a869e.

The issue with this patch, which I did sign off on, is that for the
domain member case, we already know that the SID is reasonable and
valid, and we indeed rely on that, because we keep it as an additonal
group anyway.  The primary group is not so special that we need to do
extra validation.

Calling this function may put a user into the domain 'domain users'
group, even if they are not in that group to start with.

Andrew Bartlett