tuskar-ui has been retired

With https://review.openstack.org/#/c/270850/ and
https://review.openstack.org/#/c/270854/ tuskar-ui is no longer an
active or maintained project. This patch removes it from the Horizon
project's managed repos.

Change-Id: I8a267fc66cb7955b980b7df840df16301a562f07

reference/projects.yaml

@@ -794,11 +794,6 @@ horizon:
         - release:cycle-with-intermediary
         - release:has-stable-branches
         - release:managed
-    tuskar-ui:
-      repos:
-        - openstack/tuskar-ui
-      tags:
-        - release:independent
     xstatic-angular:
       repos:
         - openstack/xstatic-angular