message: remove 27pt stencil from example overview
diff: @@ -127,12 +127,6 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  * </td></tr>
  *
  * <tr valign="top">
  - * <td>@ref twentyseven_pt_stencil_solver</td>
  - * <td> Using a twentyseven point 3D stencil to solve the poisson equation
  - * with array views.
  - * </td></tr>
  - *
  - * <tr valign="top">
  * <td>@ref external_lib_interfacing</td>
  * <td> Using Ginkgo's solver with the external library deal.II.
  * </td></tr>
  @@ -228,7 +222,6 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  * <td>@ref poisson_solver,
  * @ref three_pt_stencil_solver,
  * @ref nine_pt_stencil_solver,
  - * @ref twentyseven_pt_stencil_solver,
  * @ref custom_matrix_format
  * </td>
  * </tr>
  