rustfmt, rls, and clippy are no longer preview components

I haven't looked up when this happened, probably should specify.

This spot can be updated: https://github.com/rust-lang-nursery/edition-guide/blame/68c458b9b68edced39aebea60e672a22d4d50edf/src/rust-2018/rustup-for-managing-rust-versions.md#L148-L206

llvm-tools is still in preview; making a separate tracking issue for that.