Remove unused variable

src/scheme/AcousticSolver.hpp

@@ -322,7 +322,6 @@ class AcousticSolver
 
     CellValue<double>& ej = unknowns.ej();
     CellValue<double>& pj = unknowns.pj();
-    CellValue<double>& gammaj = unknowns.gammaj();
     CellValue<double>& cj = unknowns.cj();
 
     const CellValue<const Rd>& xj = m_mesh_data.xj();