include: drop now empty xkbfile.h

This (public) file isn't used by anybody outside Xserver tree
and doesn't contain anything useful anymore, so lets drop it.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1729>

include/meson.build

@@ -498,7 +498,6 @@ if build_xorg
             'displaymode.h',
             'window.h',
             'windowstr.h',
-            'xkbfile.h',
             'xkbsrv.h',
             'xkbstr.h',
             'xkbrules.h',