This was done in #145740 and #145947. It is causing problems for people
using r-a on anything that uses the rustc-dev rustup package, e.g. Miri,
clippy.
This repository has lots of submodules and subtrees and various
different projects are carved out of pieces of it. It seems like
`[workspace.dependencies]` will just be more trouble than it's worth.
The current `rust-version = "1.63"` was inherited from rayon, but it
doesn't make sense to limit this in the compiler workspace. Having any
setting at all has effects on tools like `cargo info` that try to infer
the MSRV when the workspace itself doesn't specify it. Since we are the
compiler, our only MSRV is whatever bootstrapping requires.
