Expand the description in systemd

In systemd, we specify removing a directory (/usr/lib/rpm).
However, we remove the /usr/bin/xsltproc file in the same block,
so expand the description.

was r11568.

chapter06/systemd.xml

@@ -189,18 +189,9 @@ meson --prefix=/usr                \
 
 <screen><userinput remap="install">LANG=en_US.UTF-8 ninja install</userinput></screen>
 
-    <para>删除一个不需要的目录：</para>
+    <para>删除不需要的目录和文件：</para>
 
 <screen><userinput remap="install">rm -rfv /usr/lib/rpm
-<!--
-    <para>创建 Sysvinit 兼容性符号链接，使 systemd 被用作默认 init 系统：
-    </para>
-
-<screen><userinput remap="install">for tool in runlevel reboot shutdown poweroff halt telinit; do
-     ln -sfv ../bin/systemctl /sbin/${tool}
-done
-ln -sfv ../lib/systemd/systemd /sbin/init</userinput></screen>
--->
 rm -f /usr/bin/xsltproc</userinput></screen>
 
     <para>创建 <command>systemd-journald</command> 需要的