Undeprecate file for now, there is no alternative at the moment

dune/fufem/surfmassmatrix.hh

 #ifndef SURFACE_MASSMATRIX_HH
 #define SURFACE_MASSMATRIX_HH
 
-#warning This file is deprecated!  Use dune/fufem/assemblers/boundaryoperatorassembler.hh instead!
+//#warning This file is deprecated!  Use dune/fufem/assemblers/boundaryoperatorassembler.hh instead!
 
 /** \file
     \brief Contains a method which assembles the FE mass matrix of a boundary patch of a grid.
+           In contrast to the boundaryoperatorassembler, this method is using local boundary indices to set
+           up the mass matrix.
 */
 
 #include <dune/geometry/quadraturerules.hh>