Keep only legacy jobs which actually test the d-g code path

Only legacy jobs test the devstack-gate code and all the zuulv3 native jobs
use the devstack only.

Many of the current job running in this gate has been converted to
zuulv3 with same name so we are running zuulv3 native job which does
not use d-g code on d-g gate.

Example: Ibe613a48116aed9cbcc7c689a50c1ef9fba60f05 migrated the neutron
greande job to zuulv3 native.

Also this remove ocata legacy job which is EOL.

To cover the testing for supporting the stable branches in d-g, we have
'legacy-tempest-neutron-full-stable' job running on last supported stable
branch (stable/wallaby - https://review.opendev.org/c/openstack/devstack-gate/+/785003).
Adding it in gate pipeline too to have 'integrated' queue testing.

Also removing the below broken jobs, they need more work to migrate to latest distro
or so but we do not have bandwidth to fix them now.
- legacy-tempest-dsvm-neutron-full-centos-7:
- legacy-tempest-dsvm-multinode-full:

We are not adding any stable branch grenade legacy job here as preparing the
one will be more work. If any issue occur for grenade legacy job side then we can
fix/test it via depends-on.

Change-Id: If7b870331cae42e3250bdf548c572f7067d835f5

.zuul.yaml

@@ -24,7 +24,6 @@
 
 - project:
     templates:
-      - integrated-gate-py3
       - official-openstack-repo-jobs
       - openstack-python35-jobs
     check:
@@ -32,32 +31,19 @@
         - openstack-tox-bashate:
             nodeset: ubuntu-bionic
         - openstack-tox-py27
-        - neutron-grenade
-        - neutron-grenade-multinode
-        - neutron-grenade-dvr-multinode:
-            voting: false
-        - legacy-tempest-dsvm-neutron-full-ocata:
-            voting: false
-        - legacy-tempest-dsvm-neutron-full-centos-7:
-            voting: false
-        - legacy-tempest-dsvm-multinode-full:
-            voting: false
         - devstack:
             files:
               - ^roles/
-        - neutron-tempest-plugin-api:
-            voting: false
         - legacy-tempest-neutron-full-stable:
             branches: ^(?!driverfixes/).*$
-            voting: false
         - devstack-gate-hooks
     gate:
       queue: integrated
       jobs:
         - openstack-tox-py27
-        - neutron-grenade
-        - neutron-grenade-multinode
         - devstack-gate-hooks
+        - legacy-tempest-neutron-full-stable:
+            branches: ^(?!driverfixes/).*$
     experimental:
       jobs:
         - legacy-tempest-dsvm-neutron-dvr-multinode-full