s4.2/fsmo.py: fixed fsmo transfer exception

s4.2/fsmo.py: fixed fsmo transfer exception

In transfer_role() there is an duplicate call to samdb.modify() inside the if statement
where the type of role is being determined (specifically for the naming fsmo). This
call is unnecessary as after the if statement their is a correct call, with a try/catch
block, used by all fsmo transfers that will handle errors - such as the DC with the
fsmo role being offline.

The call to samdb.modify() inside the if statement for naming fsmo has been removed.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10924

Signed-off-by: Steve Howells <steve.howells@moscowfirst.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Marc Muehlfeld <mmuehlfeld@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
(cherry picked from commit 9198246f91c02e33ed7a3580588557d0fb9f8811)