Remove an unused counter in MuonHoughPatternFinderTool

http://goetz.web.cern.ch/goetz/mutable_2019-06-10.html#Muon,MuGirl_Other

nightly/master/2019-06-10T2153:MuonSpectrometer/MuonReconstruction/MuonPatternFinders/MuonPatternFinderTools/MuonHoughPatternTools/MuonHoughPatternTools/MuonHoughPatternFinderTool.h +155

   153	
   154	    /** number of events counter, not in use */
   155	    mutable int        m_count;
   156	    /** use rpc preprawdata (true) */
   157	    bool       m_use_rpc;