Revert "hardcode the mutter-wayland dep for now to get a build through"
    
    There's still no cogl/clutter 1.17.x, but (X11) libmutter now depends
    on this as well, so the workaround no longer works anyway.
    
    This reverts commit afa87d93a37b3b86821a70276e0c7564b4aaaa41.