Remove extern crate rustc_macros from numerous crates.

compiler/rustc_lint_defs/src/lib.rs

@@ -1,6 +1,3 @@
-#[macro_use]
-extern crate rustc_macros;
-
 pub use self::Level::*;
 use rustc_ast::node_id::NodeId;
 use rustc_ast::{AttrId, Attribute};
@@ -11,6 +8,7 @@ use rustc_data_structures::stable_hasher::{
 use rustc_error_messages::{DiagMessage, MultiSpan};
 use rustc_hir::HashStableContext;
 use rustc_hir::HirId;
+use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::edition::Edition;
 use rustc_span::{sym, symbol::Ident, Span, Symbol};
 use rustc_target::spec::abi::Abi;