Remove useless check in AttachInterfacesTestJSON

In AttachInterfacesTestJSON, _check_interface won't do
anything if all optional params are not provided, so
this is to remove the useless _check_interface. Besides,
_test_show_interface already covers the check the author
might want to do.

Change-Id: I1a2382ed9f0c48c27017c973ba2a4831bf5a6119
diff --git a/tempest/api/compute/servers/test_attach_interfaces.py b/tempest/api/compute/servers/test_attach_interfaces.py
index e0a1d77..0248c65 100644
--- a/tempest/api/compute/servers/test_attach_interfaces.py
+++ b/tempest/api/compute/servers/test_attach_interfaces.py
@@ -103,7 +103,6 @@
                  ['interfaceAttachment'])
         iface = waiters.wait_for_interface_status(
             self.interfaces_client, server['id'], iface['port_id'], 'ACTIVE')
-        self._check_interface(iface)
         return iface
 
     def _test_create_interface_by_network_id(self, server, ifs):
@@ -190,7 +189,6 @@
         server, ifs = self._create_server_get_interfaces()
         interface_count = len(ifs)
         self.assertGreater(interface_count, 0)
-        self._check_interface(ifs[0])
 
         try:
             iface = self._test_create_interface(server)
@@ -228,7 +226,6 @@
         server, ifs = self._create_server_get_interfaces()
         interface_count = len(ifs)
         self.assertGreater(interface_count, 0)
-        self._check_interface(ifs[0])
         network_id = ifs[0]['net_id']
         self.servers_client.add_fixed_ip(server['id'], networkId=network_id)
         # Remove the fixed IP from server.