Initial signal-only overlay output for MT (ATLASSIM-3820)
This is an initial step to still support signal-only overlay output (but only when running in MT):
- remove the support from current transforms
- add output file flag and modify the existing
doSignal
->signalOnlyOutput
to make it clearer - cleanup MuonOverlay code from obsolete flag related to this
- update job options to work only with MT