Haiku Book: disable class diagrams.

The last time this was discussed on the ML, the consensus was that
the text lists were nicer than the diagrams (with only one objection).
For the minority that wants class diagrams, it's easy enough to reverse
this one-line change.

docs/user/Doxyfile

@@ -1607,7 +1607,7 @@ PERL_PATH              = /boot/home/config/bin/perl
 # this option also works with HAVE_DOT disabled, but it is recommended to
 # install and use dot, since it yields more powerful graphs.
 
-CLASS_DIAGRAMS         = YES
+CLASS_DIAGRAMS         = NO
 
 # You can define message sequence charts within doxygen comments using the \msc
 # command. Doxygen will then run the mscgen tool (see