wayland: Only send artificial mouse up events for xwayland drags

Seat has to handle two types of drags; ones where clients are updated
through data device, and xwayland version where the drag target has
mouse events sents as pointer events. A mechanism to treat them
differently was introduced, but this former xwayland hack was not
included. We also don't need to send frame events when in datadevice
mode.

This reset of pointer state breaks electron.

(cherry picked from commit 044c9f01)