Fix broken 'uses-values' links in the Porter's Handbook

The USES chapter sets an xml:id on its title tag but this doesn't
seem to generate an anchor.  As a consequence there currently are
several 'uses-values' xrefs that point to nowhere.

This is only really noticeable in the single page HTML version
(book.html) of the handbook.

PR:		227123
Reported by:	0mp
Approved by:	mat
Differential Revision:	https://reviews.freebsd.org/D15642

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

@@ -3209,7 +3209,7 @@ EXTRACT_SUFX=	.tar.gzip</programlisting>
 	<literal>USES=lha</literal> or <literal>USES=zip</literal>
 	automatically set <varname>EXTRACT_SUFX</varname> to the most
 	common archives extensions as necessary, see <xref
-	  linkend="uses-values"/> for more details.  If neither of
+	  linkend="uses"/> for more details.  If neither of
 	these are set then <varname>EXTRACT_SUFX</varname> defaults to
 	<literal>.tar.gz</literal>.</para>
 
@@ -5646,7 +5646,7 @@ RUN_DEPENDS=	${MY_DEPENDS}</programlisting>
 	  and cannot be made to work using
 	  <literal>USES=tar</literal>, <literal>USES=lha</literal> or
 	  <literal>USES=zip</literal> described in <xref
-	    linkend="uses-values"/>.</para>
+	    linkend="uses"/>.</para>
       </note>
     </sect2>
 
@@ -5679,7 +5679,7 @@ RUN_DEPENDS=	${MY_DEPENDS}</programlisting>
       <programlisting>USES= feature[:arguments]</programlisting>
 
       <para>For the complete list of values, please see
-	<xref linkend="uses-values"/>.</para>
+	<xref linkend="uses"/>.</para>
 
       <warning>
 	<para><varname>USES</varname> cannot be assigned after

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

@@ -4227,7 +4227,7 @@ USE_PYTHON=	autoplist distutils
     <para>See the <link
 	linkend="uses-tcl"><literal>USES=tcl</literal></link> and
       <link linkend="uses-tk"><literal>USES=tk</literal></link> of
-      <xref linkend="uses-values"/> for a full description of those
+      <xref linkend="uses"/> for a full description of those
       variables.  A complete list of those variables is available in
       <filename>/usr/ports/Mk/Uses/tcl.mk</filename>.</para>
   </sect1>
@@ -5015,7 +5015,7 @@ PLIST_SUB+=	VERSION="${VER_STR}"
       <para>If a specific version of Lua is needed, instructions on
 	how to select it are given in the <link
 	  linkend="uses-lua"><literal>USES=lua</literal></link> part
-	of <xref linkend="uses-values"/>.</para>
+	of <xref linkend="uses"/>.</para>
     </sect2>
 
     <sect2 xml:id="lua-defined-variables">

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

@@ -26,8 +26,7 @@
 <chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink=
   "http://www.w3.org/1999/xlink" version="5.0" xml:id="uses">
 
-  <title xml:id="uses-values">Using <varname>USES</varname>
-    Macros</title>
+  <title>Using <varname>USES</varname> Macros</title>
 
   <sect1 xml:id="uses-intro">
     <title>An Introduction to <varname>USES</varname></title>