[mechanics] remove warning with unused variable
[mechanics] remove warning with unused variable

radarsat1/siconos,bremond/siconos,bremond/siconos,radarsat1/siconos,bremond/siconos,radarsat1/siconos,radarsat1/siconos,siconos/siconos,siconos/siconos,fperignon/siconos,radarsat1/siconos,siconos/siconos,bremond/siconos,fperignon/siconos,fperignon/siconos,bremond/siconos,fperignon/siconos,siconos/siconos,fperignon/siconos