MuonReadoutGeometryR4: Fix clang warnings.
Unused variables/members. (minOne was giving a seemingly-spurious warning. However, it's not needed anyway since the default ctor for IdentifierHash initializes it as invalid.)
Unused variables/members. (minOne was giving a seemingly-spurious warning. However, it's not needed anyway since the default ctor for IdentifierHash initializes it as invalid.)