This is no longer necessary, since the SSD frames are no longer
part of Mutter process, so it is not the MetaX11Display connection
which holds the implicit grab when a mouse button is pressed over
a window frame (say, to start a drag).
As the SSD frames client communicates the same way than CSD windows
for window operations, it is also expected to undo its implicit
grab before requesting a window move/resize operation.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2683>