Stop generating class diagram and using graphviz dot in doxygen doc.

It is very slow and sometimes blocks the ci pipeline (on macos). Besides, the diagrams are not very useful in the documentation.

gen_doc/Doxyfile.in

@@ -1103,7 +1103,7 @@ PERL_PATH              =
 # fallback. It is recommended to install and use dot, since it yields more 
 # powerful graphs.
 
-CLASS_DIAGRAMS         = YES
+CLASS_DIAGRAMS         = NO
 
 # If set to YES, the inheritance and collaboration graphs will hide 
 # inheritance and usage relations if the target is undocumented 
@@ -1116,14 +1116,14 @@ HIDE_UNDOC_RELATIONS   = YES
 # toolkit from AT&T and Lucent Bell Labs. The other options in this section 
 # have no effect if this option is set to NO (the default)
 
-HAVE_DOT               = YES
+HAVE_DOT               = NO
 
 # If the CLASS_GRAPH and HAVE_DOT tags are set to YES then doxygen 
 # will generate a graph for each documented class showing the direct and 
 # indirect inheritance relations. Setting this tag to YES will force the 
 # the CLASS_DIAGRAMS tag to NO.
 
-CLASS_GRAPH            = YES
+CLASS_GRAPH            = NO
 
 # If the COLLABORATION_GRAPH and HAVE_DOT tags are set to YES then doxygen 
 # will generate a graph for each documented class showing the direct and