deprecate rustfmt-nightly crate on crates.io #5132
Description
We've been conveying the intent to do so for a while, and the existing crate hasn't been updated for a long time. That was initially because no active members of the rustfmt team had access, but we've subsequently decided that crates.io will no longer be part of rustfmt's distribution strategy.
I should now have access to the crate finally (if not I will soon), and will be deprecating the existing crate once I do.