Simplify muon trigger step dictionary
Cleanup of the muon trigger chain step dictionary (ATR-24222):
- Flatten the structure of the steps, since the [[L2 steps],[EF steps]] structure isn't actually needed
- Remove unused chain step definitions
- Consolidate the definitions with similar steps (mostly by moving the setup of the muFast/muComb steps to the getmuFast/getmuComb functions)