examples/lorawan: don't unblock IDLE mode
examples/lorawan: don't unblock IDLE mode

This is already unblocked and will trigger an assertion.
The code is still broken as other modes might be unblocked too,
but at least it is just as broken as it was before #17895

miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,miri64/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,miri64/RIOT,miri64/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kYc0o/RIOT,kaspar030/RIOT,jasonatran/RIOT,ant9000/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,jasonatran/RIOT,jasonatran/RIOT,kYc0o/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,RIOT-OS/RIOT