systemd: bump to v239

systemd: bump to v239

* remove upstreamed patches
* refresh patch 0002 which didn't apply cleanly
* update patch 0001 to catch more uses of agetty
* the README file hash has changed because some parts of this file
  were modified between v237 and v239, but the modifications are not
  related to licensing aspects

Signed-off-by: Jérémy Rosen <jeremy.rosen@smile.fr>
[Thomas: regenerate patches with less "noise", update README file
hash.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>