Remove ez_setup.py

[astrofrog]

As described in #297, ez_setup.py is deprecated. In fact, it's very rarely needed - these days virtually everyone has setuptools installed:

• If a user does pip install ..., pip requires setuptools so setuptools will be present

• If a user has conda and is doing e.g. python setup.py ..., conda environments automatically include setuptools.

• Most other major scientific packages such as Numpy, Scipy, Pandas, etc. just assume setuptools is present.

I think this is safe to remove. Once it is removed here we can update astropy-helpers in the core package and remove it there too, as well as in the package template.

Now that setuptools 1.0 has been out for a while I think it's also safe to simply remove the logic related to 'distribute' and require setuptools 1.0 or later. For user-friendliness, I've made it so that a nice error message is printed rather than a traceback.

[astropy-bot]

Hi there @astrofrog 👋 - thanks for the pull request! I'm just a friendly 🤖 that checks for issues related to the changelog and making sure that this pull request is milestoned and labeled correctly. This is mainly intended for the maintainers, so if you are not a maintainer you can ignore this, and a maintainer will let you know if any action is required on your part 😃.

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[bsipocz]

This is all very sensible, thanks @astrofrog!

[eteq]

I agree this all makes sense. Just a very minor typo in the changelog.

[eteq]

(nitpick) to be grammatically correct I think this needs to be "requiring"? Or Removing->remove.

[bsipocz]

@astrofrog - So you suggest to backport this to LTS (astropy/package-template#315 (comment)), which is fine by me. But then we also need to backport to 3.0.x otherwise the changelog will become a mess. Would that be OK with you?

[astrofrog]

Yes that sounds good, backporting to v2.0.x and v3.0.x seems like the right thing to do.