vnc: Remove scanout plane optimization

The VNC backend will place a single fullscreen surface on a virtual scanout plane, and send the entire contents of this plane every repaint.

This saves a renderer pass, but moving the mouse over the fullscreen client results in full screen damage for every mouse motion, similarly client surfact damage is ignored and every repaint pushes the entire window content over the wire.

Due to the way this is implemented, by pushing the scanout plane content from assign_planes(), the primary plane could post damage and corrupt the display.

Ideally we could fix this optimization to respect plane damage and do the scanout plane push from the repaint callback, but since a release is coming soon let's just strip it out for now.

Signed-off-by: Derek Foreman derek.foreman@collabora.com