Remove unnecesarry code in PortsAdminExtendedAttrsTest

Unnecesarry code for this test causes unessential fail.
This fix it.

Change-Id: Ia60a8460ac30546b22f8e18d685746201e028325
Closes-Bug: 1471689
diff --git a/tempest/api/network/test_ports.py b/tempest/api/network/test_ports.py
index 29600c5..06a0531 100644
--- a/tempest/api/network/test_ports.py
+++ b/tempest/api/network/test_ports.py
@@ -344,8 +344,6 @@
         super(PortsAdminExtendedAttrsTestJSON, cls).resource_setup()
         cls.network = cls.create_network()
         cls.host_id = socket.gethostname()
-        cls.tenant = cls.identity_client.get_tenant_by_name(
-            CONF.identity.tenant_name)
 
     @test.idempotent_id('8e8569c1-9ac7-44db-8bc1-f5fb2814f29b')
     def test_create_port_binding_ext_attr(self):