Decide how to display multi-locale Alphas on /download/alpha

I think the simplest solution would be to retain the current table with a single row for the multi-locale build for Alpha.

We can also add a line/paragraph of copy to the page explaining the change. As a result of removing the individual builds, the exact languages Tor Browser Alpha is available in will no longer be obvious – so we should include a list of supported locales somewhere as well.

This will need to get elevated to a support article eventually, but that can wait until this feature reaches stable in Tor Browser 12.0.

Due date is a guesstimate – we'll need to have a plan in place ahead of 12.0a4's launch by the end of the month. See tpo/applications/tor-browser-build#40627 (closed) for details.