Porter's Handbook: Stop mentioning "port submit" in Chapter 11. Upgrading a Port

It has been broken for 4 years now (see rP371562) and mentioning
is misleading at best.

Approved by:	mat
Differential Revision:	https://reviews.freebsd.org/D16701

en_US.ISO8859-1/books/porters-handbook/upgrading/chapter.xml

@@ -285,13 +285,6 @@
     <para>Send the patch following the <link
 	xlink:href="&url.articles.problem-reports;/pr-writing.html">problem
 	report submission guidelines</link>.</para>
-
-    <tip>
-      <para>The patch can be automatically generated and the PR
-	pre-filled with the contact information by using
-	<command>port submit</command>.  See <xref
-	  linkend="testing-porttools"/> for more details.</para>
-    </tip>
   </sect1>
 
   <sect1 xml:id="moved-and-updating-files">