Hmm, I was actually thinking the opposite from @astrofrog: that the docs stuff should stay in `astropy`, but the tests should be in `astropy_helpers`.  My reasoning is that the testing stuff is something you definitely want to support, as it (at least should) be an integral part of development and installing (i.e., if there's a problem, you want users to be able to run the tests no matter what).  But the docs are typically available online somewhere, so users don't need it - and the developers probably can handle installing astropy.

But when I think about it, it probably isn't *that* hard to do move both, right? I think the `sphinx` module can just be moved out basically wholesale...