This patch removes a conditional check in the update_router() method
which was verifying if snat was enabled in order to update the nat
rules. This check does not make sense in the update method as if snat
was disabled we should still call update_nat_rules() which will then
remove the NAT entry from the OVN NB DB.
(cherry picked from Neutron
Signed-off-by: Lucas Alvares Gomes <firstname.lastname@example.org>