I created a new and cleaner favicon for mesa3d.org, and it seems like a
good idea to use that one for the docs as well.
While we're at it, replace the original PNG with the original SVG asset
the ICO-file was generated from.
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5643>
Erik Faye-Lund