Remove obsolete modifiers (using TrigSteer_HLT or similarly obsolete code)

Remove Modifiers that only apply changes to TrigSteer_HLT (on its way out) or tools already removed from the release.

Some of these might be useful, but I would expect them to have been migrated at this point. Clearly they can be re-introduced if needed.

It might also be possible to go further, but this would require specific domain knowledge.