remove forward scheduler and connected components

This removes the fwd scheduler and similar components.

The Hive I/O tests are broken due to the non-thread safety of the involved I/O components. Previously they ended up in a stalled situation, now they crash instead due to the different behaviour of the AvalancheSchedulerSvc. I disabled the parallelization in these tests for now. Not sure it is worth fixing at this point. Actually one of the non-failing tests was already producing garbled output previously as the write order of events was not preserved any more, which went unnoticed.