[wwwdocs] Remove form for (un)subscribing from old mailing lists

[Jonathan Wakely]

On 24/04/20 12:57 +0200, Gerald Pfeifer wrote:
>On Thu, 23 Apr 2020, Jonathan Wakely wrote:
>> This no longer works, so direct people to the mailman listinfo pages
>> instead.
>>
>> OK to commit to wwwdocs?
>
>Yes, thank you!
>
>I was wondering whether we could keep something similar to this nice
>form, but could not come up with a good way.  So a regression we'll
>swallow as part of the system migration.

We could link directly to the listinfo page for each list, to get
there in a single click. We can add that later, for now I wanted a
quick fix for the broken form (and I've pushed that change).