Removal of HS-DAG diagnosis engine from preferences

HS-DAG implements a diagnosis calculation considering non-minimal conflict sets.

Since the available conflict searchers all provide minimal conflict sets the HS-DAG algorithm is not necessary and thus can be omitted for selection.

The algorithm implmenenting HS-DAG will remain in the code base and thus can be reactivated once non-minimal conflict searchers are implemented (eg. conflict searchers which exploits parallelism during search).