Only maintain number of rows in CSR matrix.

We will generate square matrices only in the foreseeable future and
there is no need to maintain the number of columns (the 'n' member)
separately.  Update all users accordingly.

src/ifs_tpfa.c

@@ -108,9 +108,6 @@ ifs_tpfa_construct_matrix(grid_t *G)
             }
         }
 
-        /* The tpfa matrix is square */
-        A->n = A->m;
-
         assert ((size_t) A->ia[ G->number_of_cells ] == nnz);
 
         /* Guarantee sorted rows */

src/sparse_sys.c

@@ -39,7 +39,6 @@ csrmatrix_new_count_nnz(size_t m)
 
         if (new->ia != NULL) {
             new->m   = m;
-            new->n   = 0;
             new->nnz = 0;
 
             new->ja  = NULL;
@@ -77,7 +76,6 @@ csrmatrix_new_known_nnz(size_t m, size_t nnz)
             new = NULL;
         } else {
             new->m   = m;
-            new->n   = 0;
             new->nnz = nnz;
         }
     }

src/sparse_sys.h

@@ -30,7 +30,6 @@ extern "C" {
 struct CSRMatrix
 {
     size_t      m;
-    size_t      n;
     size_t      nnz;
 
     int        *ia;