Strip the `reflect` setup.py command.

We no longer have a use for it, and I suspect that the build-time version checking will be done another way.

We could/should strip out that functionality, and everything in setup.py that existed to support it.

I think that we should, for a while, leave a reflect command that does nothing except indicate that it is deprecated. I think this because I've left quite a few messages around about running the reflect command, and I'd like it not to fail hard on people.