Remove xenial-newton tests

Xenial newton test has been failing for a few months and is almost
out of support.

Change-Id: I4a770a4ab6e5d6f857c7b5abc2f33ac574467ee1

src/tests/gate-basic-xenial-newton

@@ -1,24 +0,0 @@
-#!/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 Gnocchi Charm deployment on xenial-newton."""
-
-from basic_deployment import GnocchiCharmDeployment
-
-if __name__ == '__main__':
-    deployment = GnocchiCharmDeployment(series='xenial',
-                                        openstack='cloud:xenial-newton')
-    deployment.run_tests()