Fix duplicate dfn/subdfn for canvas's setTransform

Until recently we had only one way to call the canvas setTransform() method:
with a list of doubles. Then bb00977
overloaded the method to also accept a DOMMatrixInit object. But the change
causes a spec build error because the markup for it in the spec source causes
duplicate IDs in the generated spec output. This change de-duplicates.

source

@@ -63934,7 +63934,7 @@ try {
 
    </dd>
 
-   <dt><var>context</var> . <code subdfn data-x="dom-context-2d-setTransform">setTransform</code>(<var>matrix</var>)</dt>
+   <dt><var>context</var> . <code data-x="dom-context-2d-setTransform">setTransform</code>(<var>matrix</var>)</dt>
 
    <dd>
 
@@ -64021,8 +64021,7 @@ try {
   data-x=""><span data-x="dom-context-2d-transform">transform</span>(<var>a</var>, <var>b</var>,
   <var>c</var>, <var>d</var>, <var>e</var>, <var>f</var>)</code> method with the same arguments.</p>
 
-  <p>The <dfn><code
-  data-x="dom-context-2d-setTransform">setTransform(<var>matrix</var>)</code></dfn> method must
+  <p>The <dfn><code data-x="">setTransform(<var>matrix</var>)</code></dfn> method must
   reset the <span>current transformation matrix</span> to the value represented by the result of
   running the <span>validate and fixup</span> algorithm on <var>matrix</var>.</p>