Revise scatter forwards (#61)

As suggested in #60

Author: jorgensd

chapter2/nonlinpoisson_code.ipynb

@@ -60,7 +60,6 @@
     "u_exact = lambda x: eval(str(u_ufl))\n",
     "u_D = Function(V)\n",
     "u_D.interpolate(u_exact)\n",
-    "u_D.x.scatter_forward()\n",
     "fdim = mesh.topology.dim - 1\n",
     "boundary_facets = locate_entities_boundary(mesh, fdim, lambda x: numpy.full(x.shape[1], True, dtype=bool))\n",
     "bc = dirichletbc(u_D, locate_dofs_topological(V, fdim, boundary_facets))"
@@ -187,7 +186,6 @@
    "source": [
     "set_log_level(LogLevel.INFO)\n",
     "n, converged = solver.solve(uh)\n",
-    "uh.x.scatter_forward()\n",
     "assert(converged)\n",
     "print(f\"Number of interations: {n:d}\")"
    ]