It seems building the doxygen docs has bit-rotted over time, and now
generates a set of empty modules, apart from some basic descriptions.
Since Mesa is mostly implementing externally documented APIs, I don't
think it makes a whole lot of sense trying to fix this, and I think the
presence of these files might confuse users who try them out.
So let's just get rid of this.
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10611>