Remove variable q for StressBC

apps/gpu/LBM/BoundaryLayer/BoundaryLayer.cpp

src/gpu/GridGenerator/grid/BoundaryConditions/Side.cpp

src/gpu/GridGenerator/grid/BoundaryConditions/Side.h

src/gpu/GridGenerator/grid/BoundaryConditions/SideTest.cpp

src/gpu/GridGenerator/grid/GridBuilder/LevelGridBuilder.cpp

src/gpu/GridGenerator/grid/GridBuilder/LevelGridBuilder.h