Remove the ce:docker and ee:docker jobs as they're not needed anymore

This was originally reported on Slack by @jennielouie:

Why do we tag some end-to-end specs with :docker (or, why do we have the ce:docker and ee:docker pipeline jobs)? If the spec runs as part of a different job is the :docker tag required?

Then I replied:

Yeah it doesn’t seem useful anymore. Based on gitlab-org/charts/gitlab#1172 (comment 146032399), the problem was that some tests wrongly had the :orchestration tag. Creating the ce:docker/ee:docker jobs were mostly a “work-around” to run these tests IMO: !221 (diffs). Based on gitlab-org/charts/gitlab#1172 (comment 151670036), the :orchestration should be removed from the tests that don’t need it (and I checked, it has been removed since then), and we don’t need the ce:docker/ee:docker jobs anymore, and probably don’t need the :docker tag neither. 🤔

As a follow-up, I think we could remove the :docker tag from the scenarios.