systemd: Use upstream tmpfiles.d rules

This fixes a failing assert in systemd-timesyncd (issue #5913) as it
expects the directory /run/systemd/netif/links/ to exist, and nothing in
NixOS currently creates it.

Also we get a net reduction in our code as rules for /run/utmp and
/var/log/journal are also provided by the same upstream file.

(cherry picked from commit a278a922)