Make L1Menu generation independent of old or new TriggerFlags

In the past TriggerFlags were used to exchange information within the L1Menu generation code (like list of chains, list of thresholds, ...). This was pointless, as this information was not supposed to be configured from the outside.

The only global input was the name of the menu that is to be built. This is now a parameter of the call to build the L1 menu.