Removed the CLHEP dependence of the code.

A dependence that was not even made explicit in the CMake configuration
of the package. :-( And in any case, the value of pi can be retrieved
much more easily than by using CLHEP...

Event/xAOD/xAODTrigMuon/Root/TrigMuonDefs.cxx

+/*
+  Copyright (C) 2002-2018 CERN for the benefit of the ATLAS collaboration
+*/
+
+// Local include(s).
 #include "xAODTrigMuon/TrigMuonDefs.h"
-#include <math.h>
-#include <iostream>
+
+// System include(s).
+#include <cmath>
 
 namespace xAOD{
 
@@ -10,19 +16,19 @@ namespace L2MuonParameters{
   ECRegions whichECRegion( const float eta, const float phi ){
       float absEta = fabs(eta);
       if( ( 1.3 <= absEta && absEta < 1.45) &&
-	  ( (0                 <= fabs(phi) && fabs(phi) < CLHEP::pi/48. )     ||
-	    (CLHEP::pi*11./48. <= fabs(phi) && fabs(phi) < CLHEP::pi*13./48. ) ||
-	    (CLHEP::pi*23./48. <= fabs(phi) && fabs(phi) < CLHEP::pi*25./48. ) ||
-	    (CLHEP::pi*35./48. <= fabs(phi) && fabs(phi) < CLHEP::pi*37./48. ) ||
-	    (CLHEP::pi*47./48. <= fabs(phi) && fabs(phi) < CLHEP::pi )
+	  ( (0                 <= fabs(phi) && fabs(phi) < M_PI/48. )     ||
+	    (M_PI*11./48. <= fabs(phi) && fabs(phi) < M_PI*13./48. ) ||
+	    (M_PI*23./48. <= fabs(phi) && fabs(phi) < M_PI*25./48. ) ||
+	    (M_PI*35./48. <= fabs(phi) && fabs(phi) < M_PI*37./48. ) ||
+	    (M_PI*47./48. <= fabs(phi) && fabs(phi) < M_PI )
 	    )
 	  ) return WeakBFieldA;
       
       else if( ( 1.5 <= absEta && absEta < 1.65 ) &&
-	       ( (CLHEP::pi*3./32.  <= fabs(phi) && fabs(phi) < CLHEP::pi*5./32. ) ||
-		 (CLHEP::pi*11./32. <= fabs(phi) && fabs(phi) < CLHEP::pi*13./32.) ||
-		 (CLHEP::pi*19./32. <= fabs(phi) && fabs(phi) < CLHEP::pi*21./32.) ||
-		 (CLHEP::pi*27./32. <= fabs(phi) && fabs(phi) < CLHEP::pi*29./32.)
+	       ( (M_PI*3./32.  <= fabs(phi) && fabs(phi) < M_PI*5./32. ) ||
+		 (M_PI*11./32. <= fabs(phi) && fabs(phi) < M_PI*13./32.) ||
+		 (M_PI*19./32. <= fabs(phi) && fabs(phi) < M_PI*21./32.) ||
+		 (M_PI*27./32. <= fabs(phi) && fabs(phi) < M_PI*29./32.)
 		 )
 	       ) return WeakBFieldB;
       

Event/xAOD/xAODTrigMuon/xAODTrigMuon/TrigMuonDefs.h

 // Dear emacs, this is -*- c++ -*-
-
 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2018 CERN for the benefit of the ATLAS collaboration
 */
-
-// $Id: TrigMuonDefs.h $
 #ifndef XAODTRIGMUON_TRIGMUONDEFS_H
 #define XAODTRIGMUON_TRIGMUONDEFS_H
 
-#include "CLHEP/Units/PhysicalConstants.h"
-
 /// Namespace holding all the xAOD EDM classes
 namespace xAOD {
 
 namespace L2MuonParameters
 {
 
-    /// Define chamber types and locations                                                                                            
+    /// Define chamber types and locations
     enum Chamber {
       BarrelInner  = 0, ///< Inner station in the barrel spectrometer
       BarrelMiddle = 1, ///< Middle station in the barrel spectrometer
@@ -32,17 +27,16 @@ namespace L2MuonParameters
       MaxChamber   = 11  ///< Number of measurement point definitions
     };
 
-    ///  Define algoriths ID                                                                                                          
+    ///  Define algoriths ID
 	 enum L2MuonAlgoId{GEV900ID=0,   MUONID=1,     HALOID=2,    COSMICID=3,
                       LOOSE_HM=10,  MEDIUM_HM=11, TIGHT_HM=12, LOOSE_LM=13,
                       MEDIUM_LM=14, TIGHT_LM=15,
                       NULLID=99999};
 
     enum ECRegions{ Bulk, WeakBFieldA, WeakBFieldB};
-  
+
     ECRegions whichECRegion( const float eta, const float phi );
 }
-  
 
 }