chore: get rid of legacy e2e directory (#17960)

So these haven't been touched in over 3 years and are very outdated.
With the update to the new scaladoc UI refactor, these were never
updated. They also don't seem to be actual testing a lot apart from the
old filter bar. Looking at the comment

[here](#17401 (reply in thread)),
I agree that it's probably best to just sunset this. If someone really
wants to dig into this in the future they can look back at these, but I
think to avoid any confusion we should just remove these.

[skip test]
[skip test_windows_fast]
[skip mima]
[skip community_build]
[skip test_sbt]

refs: #17401
[Cherry-picked d332059]