Remove an instruction in man-db no longer needed

was r11398.

chapter06/man-db.xml

@@ -107,10 +107,11 @@
 
 <screen><userinput remap="install">make install</userinput></screen>
 
+<!--
     <para revision="systemd">删除一个对不存在用户的引用：</para>
 
 <screen revision="systemd"><userinput remap="install">sed -i "s:man man:root root:g" /usr/lib/tmpfiles.d/man-db.conf</userinput></screen>
-
+-->
   </sect2>
 
   <sect2>