Revert introduction of [workspace.dependencies].

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.

Author: nnethercote

rustc_public/Cargo.toml

@@ -12,9 +12,9 @@ rustc_public_bridge = { path = "../rustc_public_bridge" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
-scoped-tls.workspace = true
+scoped-tls = "1.0"
 serde = { version = "1.0.125", features = [ "derive" ] }
-tracing.workspace = true
+tracing = "0.1"
 # tidy-alphabetical-end
 
 [features]