[mutter] Non-fast-forward update to branch wip/ssd-black-borders-fix

[Ray Strode <halfline src gnome org>]

The branch 'wip/ssd-black-borders-fix' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  d4dc79e... compositor: get rid of initial black rectangle on xwayland 

Commits added to the branch:

  8904c55... compositor: get rid of initial black rectangle on xwayland