Don't mark ineffective_unstable_trait_impl as an internal lint

It's not an internal lint:
- It's not in the rustc::internal lint group
- It's on unconditionally, because it actually lints `staged_api`, not
  the compiler

This fixes a bug where `#[deny(rustc::internal)]` would warn that
`rustc::internal` was an unknown lint.

src/test/ui/stability-attribute/stability-attribute-trait-impl.rs

@@ -22,7 +22,7 @@ impl StableTrait for UnstableType {}
 impl UnstableTrait for StableType {}
 
 #[unstable(feature = "x", issue = "none")]
-//~^ ERROR an `#[unstable]` annotation here has no effect [rustc::ineffective_unstable_trait_impl]
+//~^ ERROR an `#[unstable]` annotation here has no effect [ineffective_unstable_trait_impl]
 impl StableTrait for StableType {}
 
 fn main() {}

src/test/ui/stability-attribute/stability-attribute-trait-impl.stderr

@@ -4,7 +4,7 @@ error: an `#[unstable]` annotation here has no effect
 LL | #[unstable(feature = "x", issue = "none")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `#[deny(rustc::ineffective_unstable_trait_impl)]` on by default
+   = note: `#[deny(ineffective_unstable_trait_impl)]` on by default
    = note: see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information
 
 error: aborting due to previous error