Drop trusty-liberty test as its EOL.

Change-Id: I4265c92ad7ca8ce7c924b3b861d349b0cef7529e

tests/gate-basic-trusty-liberty

-#!/usr/bin/env python
-#
-# Copyright 2016 Canonical Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#  http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-"""Amulet tests on a basic openstack-dashboard deployment on trusty-liberty."""
-
-from basic_deployment import OpenstackDashboardBasicDeployment
-
-if __name__ == '__main__':
-    deployment = OpenstackDashboardBasicDeployment(series='trusty',
-                                                   openstack='cloud:trusty-liberty',
-                                                   source='cloud:trusty-updates/liberty')
-    deployment.run_tests()