Fix tests of unsat cores (#6593)

Fix tests of unsat cores (#6593)

This updates all regressions that pass check-unsat-cores to enable check-unsat-cores. This includes any incremental benchmark, which was disabled in run_regression.py previously.

It adds --no-check-unsat-cores to a few corner benchmarks that were previously disabled based on --incremental.

It also reverts a change to when proofs are disabled: options like sygus-inference should not permit proofs (or unsat cores).