Remove mention of SGML tools

Approximately nobody is interested in them.

Fixes #11271.

Author: annevk

source

@@ -126102,7 +126102,6 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
   <dfn export>HTML parser</dfn>.</p>
 
   <div class="note">
-
    <p>While the HTML syntax described in this specification bears a close resemblance to SGML and
    XML, it is a separate language with its own parsing rules.</p>
 
@@ -126113,10 +126112,6 @@ dictionary <dfn dictionary>StorageEventInit</dfn> : <span>EventInit</span> {
    to have one representation while widely deployed web browsers interoperably implemented a
    different representation &mdash; has wasted decades of productivity. This version of HTML thus
    returns to a non-SGML basis.</p>
-
-   <p>Authors interested in using SGML tools in their authoring pipeline are encouraged to use XML
-   tools and the XML serialization of HTML.</p>
-
   </div>
 
   <p>For the purposes of conformance checkers, if a resource is determined to be in <span>the HTML