samba-tool domain provision: Remove experimental OpenLDAP support

samba-tool domain provision: Remove experimental OpenLDAP support

This feature has long been obsolete, remaining only in the hope
that it might be revived in the future.

Specifically, in 2011 the S4 OpenLDAP backend HOWTO was removed:

 commit 1d46325af8541ea467c79cd86e65f93ce6a14ff4
 Author: Andrew Bartlett <abartlet@samba.org>
 Date:   Wed Apr 27 22:42:29 2011 +1000

     Remove outdated S4 OpenLDAP backend HOWTO.

There is a project to revive this, hosted here:

https://github.com/Symas/samba
and
https://github.com/Symas/samba_overlays

However discussions at SambaXP with Nadezhda Ivanova
indicate a new approach with slapd being started by Samba
and taught to read native Samba ldb files is more likely
in the short term.

This has the advantage that Samba's provision and offline
tooling would not need to change, with the solution looking
more like how BIND9_DLZ has access to the Samba DB.

If any of this is required then reverting these patches will be
the least of the difficulties in bringing this to production.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Nadezhda Ivanova <nivanova@symas.com>