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_builtin_macros/src/env.rs

@@ -8,7 +8,7 @@ use std::env::VarError;
 
 use rustc_ast::token::{self, LitKind};
 use rustc_ast::tokenstream::TokenStream;
-use rustc_ast::{AstDeref, ExprKind, GenericArg, Mutability};
+use rustc_ast::{ExprKind, GenericArg, Mutability};
 use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
 use rustc_span::{Ident, Span, Symbol, kw, sym};
 use thin_vec::thin_vec;
@@ -148,13 +148,13 @@ pub(crate) fn expand_env<'cx>(
                         cx.dcx().emit_err(errors::EnvNotDefined::CargoEnvVar {
                             span,
                             var: *symbol,
-                            var_expr: var_expr.ast_deref(),
+                            var_expr: &var_expr,
                         })
                     } else {
                         cx.dcx().emit_err(errors::EnvNotDefined::CustomEnvVar {
                             span,
                             var: *symbol,
-                            var_expr: var_expr.ast_deref(),
+                            var_expr: &var_expr,
                         })
                     }
                 }