Editorial: clean up popover enumerated attribute table

Helps with whatwg#9832.

source

@@ -83913,30 +83913,24 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
   <table>
    <thead>
     <tr>
-     <th>Keyword</th>
-     <th>State</th>
-     <th>Brief description</th>
-    </tr>
-   </thead>
+     <th>Keyword
+     <th>State
+     <th>Brief description
    <tbody>
     <tr>
      <td><dfn attr-value for="html-global/popover"><code
-     data-x="attr-popover-auto">auto</code></dfn></td>
-     <td rowspan=2><dfn data-x="attr-popover-auto-state">auto</dfn></td>
+     data-x="attr-popover-auto">auto</code></dfn>
+     <td rowspan=2><dfn data-x="attr-popover-auto-state">auto</dfn>
      <td rowspan=2>Closes other popovers when opened; has <span data-x="popover light dismiss">light
-     dismiss</span> and responds to <span data-x="close request">close requests</span>.</td>
-    </tr>
+     dismiss</span> and responds to <span data-x="close request">close requests</span>.
     <tr>
-     <td>The empty string</td>
-    </tr>
+     <td>(The empty string)
     <tr>
      <td><dfn attr-value for="html-global/popover"><code
-     data-x="attr-popover-manual">manual</code></dfn></td>
-     <td><dfn data-x="attr-popover-manual-state">manual</dfn></td>
+     data-x="attr-popover-manual">manual</code></dfn>
+     <td><dfn data-x="attr-popover-manual-state">manual</dfn>
      <td>Does not close other popovers; does not <span data-x="popover light dismiss">light
-     dismiss</span> or respond to <span data-x="close request">close requests</span>.</td>
-    </tr>
-   </tbody>
+     dismiss</span> or respond to <span data-x="close request">close requests</span>.
   </table>
 
   <p>The attribute's <i data-x="missing value default">missing value default</i> is the <dfn