After 01.01.2021 deprecated compiler names should be removed.

Their list can be found in the setup.py of the sioworkers.
They should be removed not only from that file, but also all throughout sioworkers, including the rst documentation.
One small problem is that sio-compile standalone script uses deprecated 'default-' compiler names (in the function sio.compilers.job:main). It therefore needs some other, preferably local, constants to select default compilers for languages.
In every other place, to the best of my knowledge, the deprecated compiler names can be removed safely.

The deprecated compiler names are also present in OIOIOI (I grepped them in two places, I may have missed some). As far as I know they exist in code paths that are never taken, so there they can also be safely removed.