doc: remove directives deprecated in Doxygen 1.9.5

All these Doxygen configuration directives raise a deprecation warning
with Doxygen 1.9.5.

Since we have WARN_AS_ERROR = YES, this causes the build to fail.

Remove these deprecated directives.

I have checked the differences by first building from scratch without
this patch, and then building from scratch with this patch, and
in the latter builddir checking

$ diff -ru -x '*.md5' -x '*.pdf' ~/tmp/weston-doc-before doc

The only differences are the Doxygen config file and one .pickle file.
So it seems the generated docs are identical with Doxygen 1.9.1.

Fixes: wayland/weston#661



Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>