Remove reference to tempest-horizon repo

... because the repo has been retired[1].

[1] 7b03c9dfb97e9900abd5fc0f5e9112dce7c59a0d

Closes-Bug: #1915832
Change-Id: I96760e4e4f35b3f044ba03156a0fa449a9854b5b
(cherry picked from commit 30a8ae7e48)

run_tests.sh

@@ -103,6 +103,8 @@ if [[ "${ZUUL_PROJECT}" = "openstack/tempest" ]]; then
 fi
 
 if [ -d /home/zuul/src/opendev.org ]; then
+    # TODO(tkajinam): This should be fixed since the tempest-horizon repo
+    #                 has been retired.
     # For ubuntu we always need to deploy tempest-horizon from source
     if uses_debs; then
         if [ -d /home/zuul/src/opendev.org/openstack/tempest-horizon ]; then
@@ -128,6 +130,8 @@ if [ -d /home/zuul/src/opendev.org ]; then
         fi
     fi
 else
+    # TODO(tkajinam): This should be fixed since the tempest-horizon repo
+    #                 has been retired.
     # For ubuntu we always need to deploy tempest-horizon from source
     if uses_debs; then
         $SUDO rm -rf /tmp/openstack/tempest-horizon

zuul.d/base.yaml

@@ -48,7 +48,6 @@
       - openstack/puppet-watcher
       - openstack/puppet-zaqar
       - openstack/tempest
-      - openstack/tempest-horizon
 
 - job:
     name: puppet-openstack-integration-run-base