[sfc] Remove unused router related methods

As tempest.scenario.manager was announced stable interface in Tempest
27.0.0[1] it can be now reused in plugins.

Removed methods:
   * _update_router_admin_state

Etherpad concerning this effort:
https://etherpad.opendev.org/p/tempest-scenario-manager-cleanup

[1] https://docs.openstack.org/releasenotes/tempest

Change-Id: I8446937a3e9aeea1375b725e8bd812f663f36beb
diff --git a/neutron_tempest_plugin/sfc/tests/scenario/manager.py b/neutron_tempest_plugin/sfc/tests/scenario/manager.py
index 96a0044..04962e4 100644
--- a/neutron_tempest_plugin/sfc/tests/scenario/manager.py
+++ b/neutron_tempest_plugin/sfc/tests/scenario/manager.py
@@ -550,6 +550,7 @@
         network has, a tenant router will be created and returned that
         routes traffic to the public network.
         """
+
         if not client:
             client = self.routers_client
         if not tenant_id:
@@ -585,12 +586,6 @@
                         router['id'])
         return router
 
-    def _update_router_admin_state(self, router, admin_state_up):
-        kwargs = dict(admin_state_up=admin_state_up)
-        router = self.routers_client.update_router(
-            router['id'], **kwargs)['router']
-        self.assertEqual(admin_state_up, router['admin_state_up'])
-
     def create_networks(self, networks_client=None,
                         routers_client=None, subnets_client=None,
                         tenant_id=None, dns_nameservers=None,