replmd: Avoid redundant dsdb_get_deleted_objects_dn() checks

replmd: Avoid redundant dsdb_get_deleted_objects_dn() checks

Quite a bit of time was spent in dsdb_get_deleted_objects_dn()
processing during either a join (~9%) or a full-sync (~28%).

The problem is we're *always* doing the dsdb_get_deleted_objects_dn()
call for each object, regardless of whether it's actually deleted or
not. i.e. we were doing an expensive query and a lot of the time just
ignoring the query result.

If it's not a deleted object we're dealing with, we can just return
early and skip the unnecessary processing.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>