doc: update doxygen configuration
Update some configuration settings that will be obsolete in the new
(1.8.17) doxygen release.
@@ -2169,7 +2169,7 @@ EXTERNAL_PAGES = YES
# interpreter (i.e. the result of 'which perl').
# The default file (with absolute path) is: /usr/bin/perl.
-PERL_PATH = /usr/bin/perl
+# obsolete with 1.8.17 PERL_PATH = /usr/bin/perl
#---------------------------------------------------------------------------
# Configuration options related to the dot tool
@@ -2191,7 +2191,7 @@ CLASS_DIAGRAMS = YES
# the mscgen tool resides. If left empty the tool is assumed to be found in the
# default search path.
-MSCGEN_PATH =
+# obsolete with 1.8.17 MSCGEN_PATH =
# You can include diagrams made with dia in doxygen documentation. Doxygen will
# then run dia to produce the diagram and insert it in the documentation. The
