Remove unused tenant_id variable

As discussed in [1] we can remove some unused
code.

[1] https://review.openstack.org/304032

Trivial fix

Change-Id: I54529092fc7e0988459d04fb1dcc092ac2fe92d6
diff --git a/manila_tempest_tests/tests/scenario/manager_share.py b/manila_tempest_tests/tests/scenario/manager_share.py
index 8e5c132..fd120d1 100644
--- a/manila_tempest_tests/tests/scenario/manager_share.py
+++ b/manila_tempest_tests/tests/scenario/manager_share.py
@@ -143,18 +143,14 @@
             self.addCleanup(client.delete_access_rule, share_id, access['id'])
         return access
 
-    def _create_router_interface(self, subnet_id, client=None,
-                                 tenant_id=None, router_id=None):
+    def _create_router_interface(self, subnet_id, client=None, router_id=None):
         """Create a router interface
 
         :param subnet_id: id of the subnet
         :param client: client object
-        :param tenant_id
         """
         if not client:
             client = self.routers_client
-        if not tenant_id:
-            tenant_id = client.tenant_id
         if not router_id:
             router_id = self._get_router()['id']
         client.add_router_interface(router_id, subnet_id=subnet_id)