[Shadow DOM] (Bug 26642) Remove deepContains.

spec/shadow/index.html

@@ -1246,15 +1246,6 @@ <h3>Extensions to <code>Element</code> Interface</h3>
         </dl>
       </section>
 
-      <section>
-        <h3>Extensions to <code>Node</code> Interface</h3>
-
-        <dl class="idl" title="partial interface Node">
-          <dt>boolean deepContains(Node? other)</dt>
-          <dd>When invoked, the method <strong>must</strong> return true if <var>other</var> is an <a>inclusive deep descendant</a> of the <a>context object</a>, and false otherwise (including when <var>other</var> is null).</dd>
-        </dl>
-      </section>
-
       <section>
         <h3>The <code>content</code> element</h3>