chapter06: Fix flex description

Approved by upstream:
<http://lists.linuxfromscratch.org/pipermail/lfs-dev/2018-April/072217.html>

chapter06/flex.xml

@@ -83,7 +83,7 @@
 
       <seglistitem>
         <seg>flex, flex++ (到 flex 的链接), 以及 lex (到 flex 的链接)</seg>
-        <seg>libfl.so 和 libfl_pic.so</seg>
+        <seg>libfl.so</seg>
         <seg>/usr/share/doc/flex-&flex-version;</seg>
       </seglistitem>
     </segmentedlist>
@@ -123,7 +123,7 @@
         <term><command>lex</command></term>
         <listitem>
           <para>一个以 <command>lex</command> 仿真模式运行
-          <command>lex</command> 的脚本</para>
+          <command>lex</command> 的符号链接</para>
           <indexterm zone="ch-system-flex lex">
             <primary sortas="b-lex">lex</primary>
           </indexterm>