Dropping the py35 testing

All the integration testing has been moved to
Bionic now[1] and py3.5 is not tested runtime for
Train or stable/stein[2].

As per below ML thread, we are good to drop the py35
testing now:
http://lists.openstack.org/pipermail/openstack-discuss/2019-April/005097.html

[1] http://lists.openstack.org/pipermail/openstack-discuss/2019-April/004647.html
[2]
https://governance.openstack.org/tc/reference/runtimes/stein.html
https://governance.openstack.org/tc/reference/runtimes/train.html

Change-Id: I42bcf5bd05a5cf38444969cdb930052527372bf6

.zuul.yaml

@@ -2,6 +2,5 @@
     templates:
       - check-requirements
       - openstack-python-jobs-horizon
-      - openstack-python35-jobs-horizon
       - openstack-python36-jobs-horizon
       - release-notes-jobs-python3

setup.cfg

@@ -16,8 +16,7 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 1.6
-envlist = py27,pep8
+envlist = py27,py36,pep8
 skipsdist = True
 
 [testenv]
@@ -24,11 +24,6 @@ commands = flake8
 basepython = python3
 commands = {posargs}
 
-[testenv:py35dj20]
-basepython = python3.5
-commands = pip install django>=2.0,<2.1
-           /bin/bash run_tests.sh -N --no-pep8 {posargs}
-
 [testenv:py27integration]
 basepython = python2.7
 commands = /bin/bash run_tests.sh -N --integration --selenium-headless {posargs}