maint(sys-apps/systemd): Sync patches with upstream

Upstream has merged all of our reload bug fixes, replace local patches
with the upstream versions.

Drop the patch that removed the check for /etc/os-release. We always
initialize missing files in the initrd so it isn't needed any more.
Merge pull request #609 from marineam/systemd

maint(sys-apps/systemd): Sync patches with upstream