TrigT1NSWSimTools: fix thread-checker warnings in NTuple code
The NSW NTuple code can never be used in multi-threaded athena in its current form. Instead of trying to fix it make sure that part of the code is only used in single-threaded mode and mark the relevant variables and functions as thread-safe.
But ideally this code should really be refactored or removed if not needed anymore.
cc @fgravili