Remove usage of specific array containing number of rows per column for CSRFormatMatrix #349
Description
The number of column for a given row is stored in CSRFormatMatrix::m_matrix_rows_nb_column but it can be deduced from CSRFormatMatrix::m_matrix_rows : for a given row i, we have m_matrix_rows_nb_column[i] = m_matrix_rows[i+1] - m_matrix_rows[i].
To reduce memory consumption, we can remove this array which is only used in Hypre back-end.