Update of IsPhoton (gamma/pi0 separation) tool for Run 3.

Removal of input variables related to the Prs detector and re-training of the MLP with MCUpgrade samples. Further info at [https://indico.cern.ch/event/775165/contributions/3228378/attachments/1772402/2880628/NeutralPID_17Dec2018.pdf]

List of modified files from CaloFuture/CaloFutureTools/src/

FutureGammaPi0SeparationTool.{h, cpp}, TMV_MLP_{inner, middle, outer}.C, CaloFutureHypoEstimator.cpp, FutureGammaPi0XGBoostTool.h

Tool interface also modified, see LHCb!1814 (merged)