Actions Menu Button Example Using aria-activedescendant: fix grammar,…

… remove space key documentation

To resolve feedback in issue #383 about examples/menu-button/menu-button-actions-active-descendant.html,
made the following changes.

1. Per feedback from @annabbott, Removed documentation of space key behavior. It is optional. It can be restored if appropriate after issue #403 is resolved.
2. Adjusted grammar in keyboard table to be consistent with similar changes made for issue #384 in commit c4d70e8.

examples/menu-button/menu-button-actions-active-descendant.html

@@ -95,11 +95,11 @@ <h3 id="kbd1_label">Menu Button</h3>
           <tbody>
             <tr>
               <th><kbd>Down Arrow</kbd><br><kbd>Space</kbd><br><kbd>Enter</kbd></th>
-              <td>Open <code>menu</code> and move focus to first <code>menuitem</code></td>
+              <td>Opens <code>menu</code> and moves focus to first <code>menuitem</code></td>
             </tr>
             <tr>
               <th><kbd>Up Arrow</kbd></th>
-              <td>Open <code>menu</code> and move focus to last <code>menuitem</code></td>
+              <td>Opens <code>menu</code> and moves focus to last <code>menuitem</code></td>
             </tr>
           </tbody>
         </table>
@@ -113,7 +113,7 @@ <h3 id="kbd2_label" class="widget">Menu</h3>
           </thead>
           <tbody>
             <tr>
-              <th><kbd>Space</kbd><br><kbd>Enter</kbd></th>
+              <th><kbd>Enter</kbd></th>
               <td>
                 <ul>
                   <li>Activates the menu item, causing the <q>Last Action</q> textbox to be updated.</li>