xwayland: Drop EGLStream backend

Now that the NVIDIA proprietary driver has grown support for GBM, the EGLStream backend for NVIDIA GPUs is now superseded by the standard GBM backend in Xwayland.

This code path is therefore not used and hardly ever tested.

Remove support for EGLStream in Xwayland.

That allows for some cleanup:

$ git diff --stat origin/master
 hw/xwayland/man/Xwayland.man            |    7 -
 hw/xwayland/meson.build                 |   25 +-
 hw/xwayland/xwayland-glamor-eglstream.c | 1129 ---------------
 hw/xwayland/xwayland-glamor-gbm.c       |   82 +-
 hw/xwayland/xwayland-glamor-gbm.h       |   45 +
 hw/xwayland/xwayland-glamor.c           |  191 +--
 hw/xwayland/xwayland-glamor.h           |  102 +-
 hw/xwayland/xwayland-screen.c           |   33 +-
 hw/xwayland/xwayland-screen.h           |    5 -
 hw/xwayland/xwayland-types.h            |    1 -
 hw/xwayland/xwayland-window-buffers.c   |   13 -
 hw/xwayland/xwayland-window-buffers.h   |    1 -
 hw/xwayland/xwayland-window.c           |   11 +-
 hw/xwayland/xwayland.c                  |    6 -
 include/meson.build                     |    3 +-
 include/xwayland-config.h.meson.in      |    3 -
 meson.build                             |   15 -
 meson_options.txt                       |    2 -
 18 files changed, 110 insertions(+), 1564 deletions(-)

/cc @ekurzinger @daenzer