Deprecate API key methods

[ledell]

Now that we added OAuth support and the API key authentication scheme is no longer functional, we can deprecate the API key methods.

Current plan is to remove the api_key argument and add ... to swallow any api_key args that appear in old/outdated scripts.

[jennybc]

I think -- but I'm not sure -- that it might be easier to just eliminate the API key stuff now. If that seems to be true, do I have encouragement to pursue that / make such a PR?

[ledell]

@jennybc Yeah, there’s no use to the api key code anymore. Feel free to get rid of it!