Remove HashableExpr abstraction (#14057)

## Summary

It looks like `ComparableExpr` now implements `Hash` so we can just
remove this.

crates/ruff_python_ast/src/hashable.rs

@@ -1,40 +0,0 @@
-use std::hash::Hash;
-
-use crate::Expr;
-
-use crate::comparable::ComparableExpr;
-
-/// Wrapper around `Expr` that implements `Hash` and `PartialEq`.
-pub struct HashableExpr<'a>(&'a Expr);
-
-impl Hash for HashableExpr<'_> {
-    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
-        let comparable = ComparableExpr::from(self.0);
-        comparable.hash(state);
-    }
-}
-
-impl PartialEq<Self> for HashableExpr<'_> {
-    fn eq(&self, other: &Self) -> bool {
-        let comparable = ComparableExpr::from(self.0);
-        comparable == ComparableExpr::from(other.0)
-    }
-}
-
-impl Eq for HashableExpr<'_> {}
-
-impl<'a> From<&'a Expr> for HashableExpr<'a> {
-    fn from(expr: &'a Expr) -> Self {
-        Self(expr)
-    }
-}
-
-impl<'a> HashableExpr<'a> {
-    pub const fn from_expr(expr: &'a Expr) -> Self {
-        Self(expr)
-    }
-
-    pub const fn as_expr(&self) -> &'a Expr {
-        self.0
-    }
-}

crates/ruff_python_ast/src/lib.rs

@@ -9,7 +9,6 @@ pub use nodes::*;
 pub mod comparable;
 pub mod docstrings;
 mod expression;
-pub mod hashable;
 pub mod helpers;
 pub mod identifier;
 mod int;