Clean up zuul jobs

Individual jobs that are included in a job template were individually
defined in each queue to pull in the nova repo, but this is not needed
for running unit tests.

This removes the individual jobs so only the template defined ones are
run. It also gets rid of the openstack-tox-lower-constraints job in
favor of using the openstack-lower-constraints-jobs template.

Change-Id: Iee4ce1612d2a38585b7c5db8db71b1619216a1fa
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

.zuul.yaml

@@ -1,32 +1,5 @@
 - project:
     templates:
       - check-requirements
+      - openstack-lower-constraints-jobs
       - openstack-python3-victoria-jobs
-    check:
-      jobs:
-        - openstack-tox-lower-constraints:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-pep8:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-py36:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-py37:
-            required-projects:
-              - openstack/nova
-    gate:
-      jobs:
-        - openstack-tox-lower-constraints:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-pep8:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-py36:
-            required-projects:
-              - openstack/nova
-        - openstack-tox-py37:
-            required-projects:
-              - openstack/nova