Remove py35 job

Ussuri release has capped hacking < 3.1.0 and this repo is now at 3.2.0
and ready for victoria.

Remove py35 job.

This fixes building since zipp 3.1.0 is only available for python 3.6
and newer and upper-constraints.txt requires that version, so py35 job
fails.

Remove also unneeded install_command from tox.ini.

Change-Id: I07395f5ba167e849c936ad66936237ea9d90864e

.zuul.yaml

@@ -3,7 +3,6 @@
       - publish-openstack-docs-pti
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python35-jobs
       - openstack-python3-victoria-jobs
       - release-notes-jobs-python3
     check:

tox.ini

@@ -7,7 +7,6 @@ ignore_basepython_conflict = True
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install {opts} {packages}
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt