TrigT1NSWSimTools: simplified MM trigger workflow pt.2

As anticipated in !79056 (merged) and asked by @jojungge many months ago, this MR reduces redundant steps and removes obsolete methods/classes in MM trigger workflow. Changelog:

• Complete removal of MMT_struct.(cxx/h) garbage files and MMT_Parameters class defined there.
• Removed of all instances of detStore(). Objects are retrieved starting from keys, not anymore stored as private class members.
• Removed convoluted computations and nested structure in MMLoadVariables class. Only computation of truth quantities is left, being disabled by default.
• Digit loop moved in the main workflow, with less operations and lines.
• Fixed a wrong float to int cast when taking digit time.

This rearrangement should make code maintenance easier, as well as simplifying debug operations. As mentioned for the first part, changes will be ported to main manually.