Remove outdated reference to PCRE

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@9753 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

prologue/why.xml

@@ -327,7 +327,7 @@
         by the <application>diff</application> program.  It is needed by
         the build procedure for several LFS packages.</para>
       </listitem>
-
+<!--
       <listitem>
         <para>PCRE</para>
 
@@ -336,7 +336,7 @@
         as Perl 5.  It is a mandatory dependency of Glib, and can also be used
         by Grep.</para>
       </listitem>
-
+-->
       <listitem>
         <para>Perl</para>