MuonSensitiveDetectorsR4: fixed clang warnings

Unused variable

MuonSpectrometer/MuonPhaseII/MuonG4/MuonSensitiveDetectorsR4/src/RpcSensitiveDetector.cxx

@@ -21,9 +21,6 @@ using namespace MuonGMR4;
 using namespace CxxUtils;
 using namespace ActsTrk;
 
-namespace {
-   constexpr double tolerance = 10. * Gaudi::Units::micrometer;
-}
 // construction/destruction
 namespace MuonG4R4 {
 
@@ -186,4 +183,4 @@ const MuonGMR4::RpcReadoutElement* RpcSensitiveDetector::getReadoutElement(const
    }
    return readOutElem;
 }
-}
\ No newline at end of file
+}