Meta: Remove the data-dfn-type attribute for the :defined pseudo-class

The term is not exported, so there's no need to specify the dfn type.

source

@@ -68827,8 +68827,7 @@ contradict people?
   these selectors match HTML elements. <ref spec=SELECTORS> <ref spec=CSSUI></p>
 
   <dl>
-   <dt><dfn data-noexport="" data-dfn-type="selector"><code
-   data-x="selector-defined">:defined</code></dfn></dt>
+   <dt><dfn data-noexport=""><code data-x="selector-defined">:defined</code></dfn></dt>
    <!-- data-noexport="" is used explicitly here and for other psuedo-classes below as the script
         scraping HTML for references (Shepherd) automatically exports terms that look like
         pseudo-classes. -->