Remove AstDeref.

It's a "utility trait to reduce boilerplate" implemented for `P` and
`AstNodeWrapper`, but removing it gives a net reduction of twenty lines
of code. It's also simpler to just implement
`HasNodeId`/`HasAttrs`/`HasTokens` directly on types instead of via
`AstDeref`.

(I decided to make this change when doing some related refactoring and
the error messages involving `AstDeref` and `HasAttrs` were hard to
understand; removing it helped a lot.)

compiler/rustc_ast/src/ast.rs

@@ -308,7 +308,6 @@ impl ParenthesizedArgs {
     }
 }
 
-use crate::AstDeref;
 pub use crate::node_id::{CRATE_NODE_ID, DUMMY_NODE_ID, NodeId};
 
 /// Modifiers on a trait bound like `~const`, `?` and `!`.
@@ -2349,7 +2348,7 @@ impl Ty {
     pub fn is_maybe_parenthesised_infer(&self) -> bool {
         match &self.kind {
             TyKind::Infer => true,
-            TyKind::Paren(inner) => inner.ast_deref().is_maybe_parenthesised_infer(),
+            TyKind::Paren(inner) => inner.is_maybe_parenthesised_infer(),
             _ => false,
         }
     }