Drop the internal rustc-rayon impls

While this looks like a breaking change, it was always documented in
`Cargo.toml` as internal-only for use in the compiler:

> Internal feature, only used when building as part of rustc,
> not part of the stable interface of this crate.

That's flipped around in [rustc-rayon#14] and [rust#136149].

[rustc-rayon#14]: rust-lang/rustc-rayon#14
[rust#136149]: rust-lang/rust#136149

.github/workflows/ci.yml

@@ -25,8 +25,6 @@ jobs:
             features: quickcheck
           - rust: stable
             features: rayon
-          - rust: stable
-            features: rustc-rayon
           - rust: stable
             features: serde
           - rust: stable

Cargo.toml

@@ -22,10 +22,6 @@ serde = { version = "1.0", optional = true, default-features = false }
 borsh = { version = "1.2", optional = true, default-features = false }
 rayon = { version = "1.9", optional = true }
 
-# Internal feature, only used when building as part of rustc,
-# not part of the stable interface of this crate.
-rustc-rayon = { package = "rustc-rayon", version = "0.5", optional = true }
-
 [dependencies.hashbrown]
 version = "0.15.0"
 default-features = false

src/lib.rs

@@ -127,9 +127,6 @@ pub mod set;
 #[cfg(feature = "rayon")]
 mod rayon;
 
-#[cfg(feature = "rustc-rayon")]
-mod rustc;
-
 pub use crate::map::IndexMap;
 pub use crate::set::IndexSet;
 pub use equivalent::Equivalent;

src/macros.rs

@@ -125,7 +125,7 @@ macro_rules! double_ended_iterator_methods {
 
 // generate `ParallelIterator` methods by just forwarding to the underlying
 // self.entries and mapping its elements.
-#[cfg(any(feature = "rayon", feature = "rustc-rayon"))]
+#[cfg(feature = "rayon")]
 macro_rules! parallel_iterator_methods {
     // $map_elt is the mapping function from the underlying iterator's element
     ($map_elt:expr) => {
@@ -150,7 +150,7 @@ macro_rules! parallel_iterator_methods {
 
 // generate `IndexedParallelIterator` methods by just forwarding to the underlying
 // self.entries and mapping its elements.
-#[cfg(any(feature = "rayon", feature = "rustc-rayon"))]
+#[cfg(feature = "rayon")]
 macro_rules! indexed_parallel_iterator_methods {
     // $map_elt is the mapping function from the underlying iterator's element
     ($map_elt:expr) => {