BlocMatrixWriter.h can be deprecated

[alxbilger]

Sofa/framework/Core/src/sofa/core/behavior/BlocMatrixWriter.h can be deprecated. The approach is not widely used (only one force field). If I understood correctly, the strategy was to detect if the matrix is a compressed row sparse matrix using a dynamic_cast, to efficiently insert matrix entries. However, this is no longer needed since compressed row sparse matrices now support efficient block insertion even through the BaseMatrix interface (because of https://github.com/sofa-framework/sofa/pull/2306/files among other PRs).