Use python jobs template for Zed

The current master should be compatible with the Zed
release of the other projects. oslo.log dropped support
for py36 see related-bug

Related-Bug: 1974244
Change-Id: I5362ca355e23830bc48f61b4a580de4a5edac423

.zuul.yaml

@@ -1,6 +1,6 @@
 - project:
     templates:
-      - openstack-python3-ussuri-jobs
+      - openstack-python3-zed-jobs
       - docs-on-readthedocs
     vars:
       rtd_webhook_id: '64851'

setup.cfg

@@ -15,8 +15,6 @@ classifier =
     Programming Language :: Python
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
 
 [files]
 packages =