Remove unnecessary mutable keyword in IDPerfMonZmumu and IDPerfMuonRefitter.

InnerDetector/InDetMonitoring/InDetPerformanceMonitoring/InDetPerformanceMonitoring/IDPerfMonZmumu.h

 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef IDPERFMON_ZMUMU_H
@@ -94,9 +94,9 @@ class IDPerfMonZmumu : public AthAlgorithm
   TTree*                          m_combStacoTree;
   TTree*                          m_combMuidTree;
 
-  mutable unsigned int            m_runNumber{};
-  mutable unsigned int            m_evtNumber{};
-  mutable unsigned int            m_lumi_block{};
+  unsigned int            m_runNumber{};
+  unsigned int            m_evtNumber{};
+  unsigned int            m_lumi_block{};
 
   double m_positive_px{};
   double m_positive_py{};

InnerDetector/InDetMonitoring/InDetPerformanceMonitoring/InDetPerformanceMonitoring/IDPerfMuonRefitter.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef IDPerfMuonRefitterTER_H
@@ -43,9 +43,9 @@ class IDPerfMuonRefitter : public AthAlgorithm
   std::string m_outputTracksName;
 
 
-  mutable int m_N_Muons;
-  mutable int m_N_MuonsRefit;
-  mutable int m_N_MuonRefitFailures;
+  int m_N_Muons;
+  int m_N_MuonsRefit;
+  int m_N_MuonRefitFailures;
 
   PerfMonServices::CONTAINERS m_container;