Versions: consolidate version listing views

There are two listing views for versions in the new dashboard, which are mostly identical:

• https://beta.readthedocs.org/projects/test-builds/ -- this is the main view, it is the first thing you see when clicking on a project
• https://beta.readthedocs.org/projects/test-builds/versions/ -- this is leftover from the legacy dashboard, where the main project view is a light version listing, and this is the full version listing

I see two options:

• Drop /project/{slug}/versions/, use /project/{slug} URL as the view for listing versions
• Make the default URL for projects /project/{slug}/versions/ instead of /project/{slug}/ (which can go away, or redirect). This way the URL matches the active tab

We might wait for legacy dashboard to make this change. The two views should be mostly identical, however there might be a difference in the filters used.

• Redirect to the correct view on version form submission https://github.com/readthedocs/readthedocs.org/pull/11355
• Do away with project.views.public.project_versions. This is a function based view that is missing a few features of the normal versions listing view. This view is redundant
• Figure out what to do about the URL for this view