Remove python3.5

We had it here for stestr which has moved on.

Change-Id: I5739d6b93e47b43ad3ec3726813cc706b8775157

.zuul.yaml

@@ -24,7 +24,6 @@
       - check-requirements
       - lib-forward-testing-python3
       - openstack-lower-constraints-jobs
-      - openstack-python35-jobs
       - openstack-python3-victoria-jobs
       - publish-openstack-docs-pti
     check:

setup.cfg

@@ -5,13 +5,12 @@ author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 summary = Command Line Interface Formulation Framework
 home-page = https://docs.openstack.org/cliff/latest/
-python-requires = >=3.5
+python-requires = >=3.6
 classifier =
     Development Status :: 5 - Production/Stable
     License :: OSI Approved :: Apache Software License
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3 :: Only