systemd: drop deprecated rootlibdir, rootprefix and split-usr options

systemd: drop deprecated rootlibdir, rootprefix and split-usr options

Support for split-usr and unmerged-usr were both removed as part of the
systemd 255 release, so remove the current deprecated rootlibdir,
rootprefix and split-usr options from the recipe.

Signed-off-by: Ricardo Salveti <ricardo.salveti@oss.qualcomm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>