Remove tempest-tripleo-ui from Stein
Remove tempest-tripleo-ui from Stein

tempest-tripleo-ui is branchless and it's retired in [1],
since it's not used anywhere let's remove it from Stein.
From Train it's already removed.

[1] https://review.opendev.org/#/c/667951/

Change-Id: Id90ef752e6c7dbe528cfae9200cdcbc956b0b769

redhat-openstack/rdoinfo,javierpena/rdoinfo