Don't restart systemd-fsck@ units

Restarting them is useless since the filesystem is already
checked. Worse, restarting them causes the filesystem to be unmounted.

Also remove an override for systemd-rkill@.service which no longer
exists.

nixos/modules/system/boot/systemd.nix

@@ -829,7 +829,7 @@ in
 
     # Some overrides to upstream units.
     systemd.services."systemd-backlight@".restartIfChanged = false;
-    systemd.services."systemd-rfkill@".restartIfChanged = false;
+    systemd.services."systemd-fsck@".restartIfChanged = false;
     systemd.services."user@".restartIfChanged = false;
     systemd.services.systemd-journal-flush.restartIfChanged = false;
     systemd.services.systemd-random-seed.restartIfChanged = false;