DOC: Old scripted effort to generate C-API documentation with Doxygen

[Mukulikaa]

Recently, I found a script in the cdoc directory that generates the C-API documentation with Doxygen. We can build the documentation with make build in that directory. I was wondering if it was there for a specific purpose.

That directory also has a Doxyfile with some configurations; @rossbar pointed out that it could be confusing to have 2 doxyfiles with configuration settings (the recent one was added when we integrated Doxygen and Breathe into the project).

I'm pinging @seiko2plus in case they have any opinions on this.

[charris]

IIRC, there was an adaptation for documenting the C code with numpy docstrings using doxigen, I think @pv was the author.

[rossbar]

We discussed this a bit in the community meeting and the consensus was that this should be removed in favor of the newer Doxygen/Breathe infrastructure that was recently added (see #18884 )