Activate the old clear sky output

The rsdscs (SW downwelling radiative flux at the surface) and rldscs (LW downwelling radiative flux at the surface) can be reverted (see this commit) to the previous erroneous EC-Earth3 CMIP6 state in order to produce comparable output with earlier CMIP6 experiments if one wishes #772. Just run:

 cd ece2cmor/scripts
 ./switch-on-off-old-clear-sky-output.py activate-old-clear-sky-output

And for deactivateing run:

 cd ece2cmor/scripts
 ./switch-on-off-old-clear-sky-output.py deactivate-old-clear-sky-output