Disable centos7 molecule test for tripleo-repos

As seen at [1] this has started failing again now for get-hash.
If I skip c7 from the get-hash molecule then nothing else will run
they are already skipped. So instead just remove the c7 job for
now. TBD if we can/want to continue supporting python2.

Our CI centos7 jobs are using py3 already.

[1] https://zuul.opendev.org/t/openstack/build/a1d1693e963b42e3ae1e9cb44ea1f190

Change-Id: I4f8121c57c80d68a4233a4bc86fa86dc0f120913

molecule/default/molecule.yml

@@ -6,8 +6,9 @@ driver:
 platforms:
   - name: instance
     image: quay.io/centos/centos:stream8
-  - name: instance_c7
-    image: quay.io/centos/centos:centos7
+# Disabled for now TBD if we will/can add python2 support.
+#  - name: instance_c7
+#    image: quay.io/centos/centos:centos7
 provisioner:
   name: ansible
 verifier: