test: Drop selenium tests for docker
test: Drop selenium tests for docker

We are not shipping cockpit-docker to Fedora 31, nor to any RHEL, which were
the only places, where we tested it.
Also cockpit-docker is in a maintenance mode, so just verify tests will
suffice.

Closes #13504
moraleslazaro/cockpit,cockpituous/cockpit,deryni/cockpit,garrett/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,deryni/cockpit,deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpituous/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,cockpituous/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,garrett/cockpit,deryni/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,deryni/cockpit,deryni/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit