adapt to latest DoxyGen version

Doxyfile

@@ -319,22 +319,6 @@ INLINE_SIMPLE_STRUCTS  = YES
 
 TYPEDEF_HIDES_STRUCT   = YES
 
-# The SYMBOL_CACHE_SIZE determines the size of the internal cache use to
-# determine which symbols to keep in memory and which to flush to disk.
-# When the cache is full, less often used symbols will be written to disk.
-# For small to medium size projects (<1000 input files) the default value is
-# probably good enough. For larger projects a too small cache size can cause
-# doxygen to be busy swapping symbols to and from disk most of the time
-# causing a significant performance penalty.
-# If the system has enough physical memory increasing the cache will improve the
-# performance by keeping more symbols in memory. Note that the value works on
-# a logarithmic scale so increasing the size by one will roughly double the
-# memory usage. The cache size is given by this formula:
-# 2^(16+SYMBOL_CACHE_SIZE). The valid range is 0..9, the default is 0,
-# corresponding to a cache size of 2^16 = 65536 symbols.
-
-SYMBOL_CACHE_SIZE      = 2
-
 # Similar to the SYMBOL_CACHE_SIZE the size of the symbol lookup cache can be
 # set using LOOKUP_CACHE_SIZE. This cache is used to resolve symbols given
 # their name and scope. Since this can be an expensive process and often the
@@ -1611,15 +1595,6 @@ HAVE_DOT               = YES
 
 DOT_NUM_THREADS        = 0
 
-# By default doxygen will use the Helvetica font for all dot files that
-# doxygen generates. When you want a differently looking font you can specify
-# the font name using DOT_FONTNAME. You need to make sure dot is able to find
-# the font, which can be done by putting it in a standard location or by setting
-# the DOTFONTPATH environment variable or by setting DOT_FONTPATH to the
-# directory containing the font.
-
-DOT_FONTNAME           = FreeSans
-
 # The DOT_FONTSIZE tag can be used to set the size of the font of dot graphs.
 # The default size is 10pt.