Remove karborclient - fix Zuul project definition

Karbor was retired.
Zuul fails to run jobs defined here due to:
  Unknown projects: openstack/python-karborclient [1]
As python-karborclient no longer has any Zuul definition.

Found trying to get [2] to do something.

Thanks to Clark Boylan (clarkb) for his quick support on #opendev.

[1] https://zuul.opendev.org/t/openstack/config-errors
[2] https://review.opendev.org/c/openstack/python-masakariclient/+/778513

Change-Id: I1237570e8af6c9af880b824e9e32e0b7dc54bc77

.zuul.yaml

@@ -14,7 +14,6 @@
       - openstack/python-heatclient
       - openstack/python-ironic-inspector-client
       - openstack/python-ironicclient
-      - openstack/python-karborclient
       - openstack/python-mistralclient
       - openstack/python-muranoclient
       - openstack/python-neutronclient