Migrate particle flow subtraction tools to one tool
requested to merge atlas-particleflow-software/athena:mhodgkin_mergeSubtractionAlgporithms_V3 into master
This update removes PFCellLevelSubtractionTool and PFRecoverSpitShowerTool, which are replaced by PFSubtractionTool. Much of the code in both was the same and so this update removes code duplication, as well as making it clearer as to what is done in each scenario. I tested that the offline output FE 4-vector are identical in 1000 mc16 ttbar events. RunTier0Tests.py shows no changes too.