Draft: smbd: map the SMBXSRV_VERSION_X from the cluster level

The cluster functional level introduced in 4.25 already provides everything smbXsrv_version_global.tdb was built for. Remove it. smbXsrv_version_global_current() becomes a plain mapping from the active cluster functional level onto the record version, and smbXsrv_version_global_init() goes away together with the database.

https://bugzilla.samba.org/show_bug.cgi?id=16256