[io] Remove deprecated function

dumux/io/vtkoutputmodule.hh

@@ -129,15 +129,6 @@ public:
     //! Do not call these methods after initialization i.e. _not_ within the time loop
     //////////////////////////////////////////////////////////////////////////////////////////////
 
-    //! Output a scalar volume variable
-    //! \param name The name of the vtk field
-    //! \param f A function taking a VolumeVariables object and returning the desired scalar
-    DUNE_DEPRECATED_MSG("Will be removed after next release. Please use addVolumeVariable(function, name) instead!")
-    void addSecondaryVariable(const std::string& name, std::function<Scalar(const VolumeVariables&)>&& f)
-    {
-        volVarScalarDataInfo_.push_back(VolVarScalarDataInfo{f, name});
-    }
-
     //! Output a scalar volume variable
     //! \param name The name of the vtk field
     //! \param f A function taking a VolumeVariables object and returning the desired scalar