- remove directory class

Differential Revision:	https://reviews.freebsd.org/D1737
Approved by:	wblock (mentor)

en_US.ISO8859-1/books/arch-handbook/boot/chapter.xml

@@ -71,10 +71,10 @@ $FreeBSD$
       activity.  Not only must code be written for every computer
       architecture, but there may also be multiple types of booting on
       the same architecture.  For example, a directory listing of
-      <filename class="directory">/usr/src/sys/boot</filename>
+      <filename>/usr/src/sys/boot</filename>
       reveals a great amount of architecture-dependent code.  There is
       a directory for each of the various supported architectures.  In
-      the x86-specific <filename class="directory">i386</filename>
+      the x86-specific <filename>i386</filename>
       directory, there are subdirectories for different boot standards
       like <filename>mbr</filename> (Master Boot Record),
       <filename>gpt</filename> (<acronym>GUID</acronym> Partition