xserver-xorg: remove sub-package ${PN}-xwayland

xserver-xorg: remove sub-package ${PN}-xwayland

xwayland has been split to a standalone package via commit

* 4ee66f574 Drop XWayland DDX

https://gitlab.freedesktop.org/xorg/xserver/-/commit/4ee66f574

and there is a recipe for xwayland in oe-core too. So remove sub-package
${PN}-xwayland from xserver-xorg accordingly.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>