tests: fix warning

Building CXX object tests/CMakeFiles/testDeviceSettings.dir/testDeviceSettings.cpp.o
/home/travis/build/ralovich/antpm/src/tests/testDeviceSettings.cpp: In member function â€˜void convert_0::test_method()â€™:
/home/travis/build/ralovich/antpm/src/tests/testDeviceSettings.cpp:73:17: warning: unused variable â€˜sâ€™ [-Wunused-variable]
/home/travis/build/ralovich/antpm/src/tests/testDeviceSettings.cpp:74:17: warning: unused variable â€˜tâ€™ [-Wunused-variable]