xwayland/eglstream: Remove stream validity

To avoid an EGL stream in the wrong state, if the window pixmap changed
before the stream was connected, we would still keep the pending stream
but mark it as invalid. Once the callback is received, the pending would
be simply discarded.

But all of this is actually to avoid a bug in egl-wayland, there should
not be any problem with Xwayland destroying an EGL stream while the
compositor is still using it.

With that bug now fixed in egl-wayland 1.1.7, we can safely drop all
that logic from Xwayland EGLstream backend.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Closes: xorg/xserver#1189
5 jobs for issue1189 in 5 minutes and 14 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Docker Image
passed debian-buster #11402789

00:00:25

 
  Build And Test
passed autotools #11402790

00:04:49

passed meson #11402791

00:02:09

passed meson-noglamor #11402792

00:01:08

passed mingw-cross-build #11402793

00:00:44