Skip centos-7 wheel builder for now

Focus on getting ubuntu working first, once working we can then switch
to centos-7. This way we can focus on 1 distro at a time.

Change-Id: I5c6b48f127a7fbc5221a88bba06e461d4846a56c
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

zuul.yaml

@@ -538,8 +538,6 @@
         label: ubuntu-xenial
       - name: wheel-mirror-ubuntu-trusty-python2
         label: ubuntu-trusty
-      - name: wheel-mirror-centos-7-python2
-        label: centos-7
       - name: wheel-mirror-ubuntu-xenial-python3
         label: ubuntu-xenial
       - name: wheel-mirror-ubuntu-trusty-python3