Revert "Use workspace lints for crates in compiler/ #138084"

Revert <https://github.com/rust-lang/rust/pull/138084> to buy time to
consider options that avoids breaking downstream usages of cargo on
distributed `rustc-src` artifacts, where such cargo invocations fail due
to inability to inherit `lints` from workspace root manifest's
`workspace.lints` (this is only valid for the source rust-lang/rust
workspace, but not really the distributed `rustc-src` artifacts).

This breakage was reported in
<https://github.com/rust-lang/rust/issues/138304>.

This reverts commit 48caf81484, reversing
changes made to c6662879b2.

Cargo.toml

@@ -63,20 +63,6 @@ exclude = [
   "src/tools/x",
 ]
 
-# These lints are applied to many crates in the workspace. In practice, this is
-# all crates under `compiler/`.
-#
-# NOTE: rustc-specific lints (e.g. `rustc::internal`) aren't supported by
-# Cargo. (Support for them is possibly blocked by #44690 (attributes for
-# tools).) Those lints are instead specified for `compiler/` crates in
-# `src/bootstrap/src/core/builder/cargo.rs`.
-[workspace.lints.rust]
-# FIXME(edition_2024): Change this to `-Wrust_2024_idioms` when all of the
-# individual lints are satisfied.
-keyword_idents_2024 = "warn"
-unreachable_pub = "warn"
-unsafe_op_in_unsafe_fn = "warn"
-
 [profile.release.package.rustc-rayon-core]
 # The rustc fork of Rayon has deadlock detection code which intermittently
 # causes overflows in the CI (see https://github.com/rust-lang/rust/issues/90227)