move service to /usr

etc/systemd/system/mount-nix-prepare.service

@@ -1,20 +0,0 @@
-[Unit]
-Description=Prepare nix mount points
-
-[Service]
-Type=oneshot
-ExecStartPre=chattr -i /
-ExecStart=/bin/sh -c "mkdir -p /nix"
-ExecStart=/bin/sh -c "mkdir -p /var/lib/nix"
-ExecStart=/bin/sh -c "mount --bind /var/lib/nix /nix"
-# We need to restart systemd and load the nix-daemon again
-# as the nix-daemon files are actually inside the /nix folder
-# which hasn't been mounted until now
-ExecStart=/bin/sh -c "systemctl daemon-reload"
-# This will fail the first time as we haven't installed nix yet
-ExecStart=-/bin/sh -c "systemctl start nix-daemon.socket"
-ExecStopPost=chattr +i /
-
-[Install]
-WantedBy=local-fs.target
-