Revert "doc/mailing-list-faq: Mention current problem with GMX"

mails to GMX seem working again

This reverts commit cd11fbcfb0.

doc/mailing-list-faq.texi

@@ -358,10 +358,6 @@ often not aware of this and is often out of their control.
 When possible we attempt to notify the provider to be removed from the
 blacklists or filters.
 
-Currently (End April/May 2020) GMX is apparently blocking all mails from FFmpeg.
-If you have a gmx account, do not hesitate to complain to them about this. We so far
-have had no luck.
-
 @section Why are my sent messages not showing up?
 
 Excluding @ref{Why is my message awaiting moderator approval?, messages that are held in the moderation queue}