Removed deprecated Doxygen options.

docs/Doxyfile.in

@@ -1467,18 +1467,6 @@ GENERATE_XML           = NO
 
 XML_OUTPUT             = xml
 
-# The XML_SCHEMA tag can be used to specify an XML schema,
-# which can be used by a validating XML parser to check the
-# syntax of the XML files.
-
-XML_SCHEMA             =
-
-# The XML_DTD tag can be used to specify an XML DTD,
-# which can be used by a validating XML parser to check the
-# syntax of the XML files.
-
-XML_DTD                =
-
 # If the XML_PROGRAMLISTING tag is set to YES Doxygen will
 # dump the program listings (including syntax highlighting
 # and cross-referencing information) to the XML output. Note that