Treewide: Remove doxygen config files and targets

In the last coreboot leadership meeting, the doxygen documentation was
declared to be dead.  Remove it.

Doxygen style comments can still be added to files, and we may generate
doxygen based documentation, but it won't be for the entire project, but
instead just for those individual areas where it is being maintained.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I8983a20793786a18d2331763660842fea836aa2a
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64228
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/commonlib/include/commonlib/console/post_codes.h

@@ -20,8 +20,7 @@
  * DOCUMENTATION:
  * Please document any and all post codes using Doxygen style comments. We
  * want to be able to generate a verbose enough documentation that is useful
- * during debugging. Failure to do so will result in your patch being rejected
- * without any explanation or effort on part of the maintainers.
+ * during debugging.
  *
  */