Remove depricated doxygen config statements.

docs/Doxyfile.in

@@ -206,7 +206,6 @@ TREEVIEW_WIDTH         = 250
 EXT_LINKS_IN_WINDOW    = NO
 HTML_FORMULA_FORMAT    = png
 FORMULA_FONTSIZE       = 10
-FORMULA_TRANSPARENT    = YES
 FORMULA_MACROFILE      =
 USE_MATHJAX            = NO
 MATHJAX_FORMAT         = HTML-CSS
@@ -312,8 +311,6 @@ DIA_PATH               =
 HIDE_UNDOC_RELATIONS   = YES
 HAVE_DOT               = YES
 DOT_NUM_THREADS        = 0
-DOT_FONTNAME           = Helvetica
-DOT_FONTSIZE           = 10
 DOT_FONTPATH           =
 CLASS_GRAPH            = YES
 COLLABORATION_GRAPH    = NO
@@ -337,7 +334,6 @@ MSCFILE_DIRS           =
 DIAFILE_DIRS           =
 DOT_GRAPH_MAX_NODES    = 50
 MAX_DOT_GRAPH_DEPTH    = 0
-DOT_TRANSPARENT        = NO
 DOT_MULTI_TARGETS      = NO
 GENERATE_LEGEND        = YES
 DOT_CLEANUP            = YES