Remove a redundant reference to ports/package section.

svn path=/head/; revision=21571

en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml

@@ -2061,8 +2061,7 @@ net.link.ether.bridge.ipfw=1</programlisting>
   	    3.0</application> is not part of the base
 	    system.  You will first need to install the
 	    <filename role="package">net/isc-dhcp3-server</filename> port or the
-	    corresponding package.  Please refer to <xref linkend="ports">
-	    for general information about ports and packages.</para>
+	    corresponding package.</para>
 
 	  <para>Once <application>ISC DHCP</application> is installed, it
 	    needs a configuration file to run, (normally named