Remove `CONTRIBUTORS` file

[jsheunis]

https://github.com/datalad/datalad-extension-template/blob/main/CONTRIBUTORS

Seems like it's not used for anything.

[adswa]

I get that it isn't used in this extension-template, but in the end, its a template, and one wouldn't want to end up with the template-contributors in one's own extension, right?
As such, the fact that it isn't used here is in my personal opinion a pretty sane thing.
As for the question of "it is useful to have for others" I checked the cookiecutter template for Python packages (https://github.com/audreyfeldroy/cookiecutter-pypackage.git), which also includes a CONTRIBUTORS file by default. And the "community standards" tabs on GitHub settings of projects (e.g., https://github.com/datalad/datalad/community) rewards one with a green tickmark when a repository ships with this file. Its also one of the easiest and lowest-effort-technology wise option to credit contributors (i.e. no bot or workflow involved, plus directly shipped with the sourcecode in plain text - no git-log parsing or github graph viewing necessary). So I would argue against the proposal to remove it.

[jsheunis]

These sound like very sane reasons that I didn't consider enough, so I'm happy to change my mind on this.

Just because I'm pedantic:

the cookiecutter template for Python packages (https://github.com/audreyfeldroy/cookiecutter-pypackage.git), which also includes a CONTRIBUTORS file by default.

And the "community standards" tabs on GitHub settings of projects (e.g., https://github.com/datalad/datalad/community) rewards one with a green tickmark when a repository ships with this file.

In both these cases there's a CONTRIBUTING.md file, but no CONTRIBUTORS file.