Remove extern crate rustc_macros from numerous crates.

compiler/rustc_expand/src/errors.rs

@@ -1,6 +1,6 @@
 use rustc_ast::ast;
 use rustc_errors::codes::*;
-use rustc_macros::Diagnostic;
+use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::Limit;
 use rustc_span::symbol::{Ident, MacroRulesNormalizedIdent};
 use rustc_span::{Span, Symbol};

compiler/rustc_expand/src/lib.rs

@@ -16,9 +16,6 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(internal_features)]
 
-#[macro_use]
-extern crate rustc_macros;
-
 #[macro_use]
 extern crate tracing;
 

compiler/rustc_expand/src/mbe.rs

@@ -14,6 +14,7 @@ pub(crate) mod transcribe;
 use metavar_expr::MetaVarExpr;
 use rustc_ast::token::{Delimiter, NonterminalKind, Token, TokenKind};
 use rustc_ast::tokenstream::{DelimSpacing, DelimSpan};
+use rustc_macros::{Decodable, Encodable};
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
 

compiler/rustc_expand/src/mbe/diagnostics.rs

@@ -8,6 +8,7 @@ use rustc_ast::token::{self, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, Diag, DiagCtxt, DiagMessage};
+use rustc_macros::Subdiagnostic;
 use rustc_parse::parser::{Parser, Recovery};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::Ident;

compiler/rustc_expand/src/mbe/metavar_expr.rs

@@ -3,6 +3,7 @@ use rustc_ast::tokenstream::{RefTokenTreeCursor, TokenStream, TokenTree};
 use rustc_ast::{LitIntType, LitKind};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, PResult};
+use rustc_macros::{Decodable, Encodable};
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::Ident;
 use rustc_span::Span;