Fix cleanup systemd-run deadlock

Problem:
Cleanup script uses systemd-run with both --wait and
--property="After=pulse-sensor-cleanup.service", creating a circular
dependency:
- cleanup.service runs and waits for uninstaller to complete
- uninstaller has After=cleanup.service, so it waits for cleanup to finish
- Result: Both services stuck waiting for each other

Fix:
Remove the --property="After=pulse-sensor-cleanup.service" line. The
Conflicts=pulse-sensor-proxy.service is sufficient to ensure the proxy
stops before uninstallation. The cleanup script doesn't need to finish
before the uninstaller starts.

Testing:
Cleanup now completes successfully, removing all artifacts:
- Systemd units removed
- Binaries deleted from /opt/pulse/sensor-proxy/
- Data directory /var/lib/pulse-sensor-proxy/ removed
- SSH keys cleaned from authorized_keys
- pulse-monitor user and API tokens deleted
- LXC bind mounts removed from container configs

Related to #605 (temperature monitoring cleanup)

scripts/install-sensor-proxy.sh

@@ -1924,7 +1924,6 @@ except: pass
                     --unit="${UNINSTALL_UNIT}" \
                     --property="Type=oneshot" \
                     --property="Conflicts=pulse-sensor-proxy.service" \
-                    --property="After=pulse-sensor-cleanup.service" \
                     --collect \
                     --wait \
                     --quiet \