All developers now use gitlab, don't confuse newcomers by suggesting
they might use the mailing list. We want everyone to use gitlab so
that patches get run through basic CI before they are merged.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Dylan Baker <dylan@pnwbakers.com>