etc: Remove Systemd hardening options unsupported in user mode (#5788)

etc/linux-systemd/user/syncthing.service

@@ -9,8 +9,6 @@ SuccessExitStatus=3 4
 RestartForceExitStatus=3 4
 
 # Hardening
-ProtectSystem=full
-PrivateTmp=true
 SystemCallArchitectures=native
 MemoryDenyWriteExecute=true
 NoNewPrivileges=true