s3-auth: Remove security=share (depricated since 3.6).

s3-auth: Remove security=share (depricated since 3.6).

This patch removes security=share, which Samba implemented by matching
the per-share password provided by the client in the Tree Connect with
a selection of usernames supplied by the client, the smb.conf or
guessed from the environment.

The rationale for the removal is that for the bulk of security=share
users, we just we need a very simple way to run a 'trust the network'
Samba server, where users mark shares as guest ok.  This is still
supported, and the smb.conf options are documented at
https://wiki.samba.org/index.php/Public_Samba_Server

At the same time, this closes the door on one of the most arcane areas
of Samba authentication.

Naturally, full user-name/password authentication remain available in
security=user and above.

This includes documentation updates for username and only user, which
now only do a small amount of what they used to do.

Andrew Bartlett

                       --------------
                      /              \
                     /      REST      \
                    /        IN        \
                   /       PEACE        \
                  /                      \
                  |      SEC_SHARE       |
                  |    security=share    |
                  |                      |
                  |                      |
                  |       5 March        |
                  |                      |
                  |        2012          |
                 *|     *  *  *          | *
        _________)/\\_//(\/(/\)/\//\/\///|_)_______