Removed obsolete functions from the reference.

[SVN r13474]

doc/reference/empty.htm

@@ -49,10 +49,6 @@
 
 <hr>
 
-<h2><a name="BOOST_PREPROCESSOR_EMPTY">#define BOOST_PREPROCESSOR_EMPTY</a>()</h2>
- <p>Obsolete. Use <a href="empty.htm#BOOST_PP_EMPTY">BOOST_PP_EMPTY</a>().</p> 
-<hr>
-
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