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.

compiler/rustc_serialize/Cargo.toml

@@ -5,14 +5,14 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-indexmap.workspace = true
+indexmap = "2.0.0"
 rustc_hashes = { path = "../rustc_hashes" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
-thin-vec.workspace = true
+thin-vec = "0.2.12"
 # tidy-alphabetical-end
 
 [dev-dependencies]
 # tidy-alphabetical-start
 rustc_macros = { path = "../rustc_macros" }
-tempfile.workspace = true
+tempfile = "3.2"
 # tidy-alphabetical-end