bots: Stop installing docker on rhel-x
bots: Stop installing docker on rhel-x

We already don't build cockpit-docker on rhel-x and don't test it there
(commit 4c789ced386daf), so actually stop installing it. It fails to
start in recent rhel-x nightlies, which makes image builds fail.

mvollmer/cockpit,martinpitt/cockpit,andreasn/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,andreasn/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,garrett/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,andreasn/cockpit,deryni/cockpit,cockpituous/cockpit,martinpitt/cockpit,andreasn/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,deryni/cockpit,andreasn/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpituous/cockpit,deryni/cockpit,garrett/cockpit,cockpituous/cockpit,cockpit-project/cockpit,cockpituous/cockpit,andreasn/cockpit,andreasn/cockpit,deryni/cockpit,martinpitt/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit