xwayland: Move xwl_surface_damage definition to xwayland-screen.c

It was already declared in xwayland-screen.h, and only takes a screen
parameter, no window ones.

Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
4 jobs for xwayland-cleanups in 4 minutes and 46 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #3483990
debian-testing

00:00:18

 
  Build And Test
passed #3483991
autotools

00:04:28

passed #3483992
meson

00:01:10

passed #3483993
meson-noglamor

00:00:42