Remove an unneded instruction

was r11548.

chapter06/tar.xml

@@ -40,10 +40,6 @@
   <sect2 role="installation">
     <title>安装 Tar</title>
 
-    <para>修复 tar-1.31 引入的一个 bug：</para>
- 
- <screen><userinput remap="pre">sed -i 's/abort.*/FALLTHROUGH;/' src/extract.c</userinput></screen>
-
     <para>准备编译 Tar：</para>
 
 <screen><userinput remap="configure">FORCE_UNSAFE_CONFIGURE=1  \