Address review comments

compiler/rustc_pattern_analysis/src/lib.rs

@@ -79,12 +79,8 @@ pub struct MatchArm<'p, Cx: MatchCx> {
 
 impl<'p, Cx: MatchCx> Copy for MatchArm<'p, Cx> {}
 
-#[cfg(not(feature = "rustc"))]
 pub trait Captures<'a> {}
-#[cfg(not(feature = "rustc"))]
 impl<'a, T: ?Sized> Captures<'a> for T {}
-#[cfg(feature = "rustc")]
-pub use rustc_data_structures::captures::Captures;
 
 /// The entrypoint for this crate. Computes whether a match is exhaustive and which of its arms are
 /// useful, and runs some lints.