CI - remove unused required-projects

openstack/requirements is not used.
openstack/kolla is used conditionally when Zuul itself adds it
due to dependency.
No need to always clone the two repositories.

Change-Id: Iabfc25e2b4227ae227f06ab196ca544b02e7808f
Signed-off-by: Radosław Piliszek <radoslaw.piliszek@gmail.com>

zuul.d/base.yaml

@@ -7,9 +7,7 @@
     attempts: 1
     timeout: 7200
     required-projects:
-      - openstack/kolla
       - openstack/kolla-ansible
-      - openstack/requirements
     irrelevant-files:
       - ^.*\.rst$
       - ^doc/.*