Stop checking installation on ubuntu-xenial nodes

It doesn't have py3.6 and we do not want to use third-party repos

Change-Id: I93bc22784b332bd039c6d6041d89802d7669d4e1

.zuul.d/zuul.yaml

@@ -5,11 +5,6 @@
     run: tests/ci/playbooks/rally-install/run.yaml
     timeout: 1800
 
-- job:
-    name: rally-install-ubuntu-xenial
-    parent: rally-install-base
-    nodeset: ubuntu-xenial
-
 - job:
     name: rally-install-ubuntu-bionic
     parent: rally-install-base
@@ -57,7 +52,6 @@
         - rally-tox-functional-py38
         - rally-tox-self
         - rally-database-migration
-        - rally-install-ubuntu-xenial
         - rally-install-ubuntu-bionic
         - rally-install-centos-7
         - rally-install-centos-8
@@ -72,7 +66,6 @@
         - rally-tox-functional
         - rally-tox-self
         - rally-database-migration
-        - rally-install-ubuntu-xenial
         - rally-install-ubuntu-bionic
         - rally-install-centos-7
         - rally-install-centos-8

setup.py

@@ -13,16 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
 
 setuptools.setup(
     setup_requires=['pbr>=1.8'],