Remove reference to integrating stylesheet Links

Closes #4224. That issue was about the general lack of specification for the Link header, which has been resolved. #8741 tracks potentially adding Link header support for rel=stylesheet, but there's no need to retain notices in the spec about the possibility of this nonstandard feature. (The note was also quite incomplete, as it didn't talk about things like the cascade, document.styleSheets, etc.)

Author: domenic

source

@@ -14980,13 +14980,6 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
   processing options</span>. This algorithm defines whether and how they react to appearing in an
   HTTP `<code data-x="http-link">Link</code>` response header.</p>
 
-  <p class="XXX">The processing of `<code data-x="http-link">Link</code>` headers is not defined for
-  all link relation types. In particular some implementations might process types that have a no-op
-  <span>process link headers</span> algorithm, and in doing so influence a <code>Document</code>'s
-  <span>script-blocking style sheet counter</span>. See
-  <a href="https://github.com/whatwg/html/issues/4224">issue #4224</a> for discussion on
-  integrating this into the spec.</p>
-
   <p>A <dfn>link processing options</dfn> is a <span>struct</span>. It has the following
   <span data-x="struct item">items</span>:</p>
 
@@ -17038,8 +17031,8 @@ console.log(style.disabled); // false</code></pre>
   </ul>
 
   <p class="XXX">It is expected that counterparts to the above rules also apply to
-  <code>&lt;?xml-stylesheet?></code> PIs and HTTP `<code data-x="http-link">Link</code>` headers.
-  However, this has not yet been thoroughly investigated.</p>
+  <code>&lt;?xml-stylesheet?></code> PIs. However, this has not yet been thoroughly
+  investigated.</p>
 
   <p>A <code>Document</code> has a <dfn>script-blocking style sheet counter</dfn>, which is a
   number, initially 0.</p>