Remove extern crate rustc_middle from numerous crates.

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -11,6 +11,7 @@ use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{self, FieldPat, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{self, FieldDef, OpaqueTypeKey, Ty, TyCtxt, TypeVisitableExt, VariantDef};
+use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
 use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
 use rustc_target::abi::{FieldIdx, Integer, VariantIdx, FIRST_VARIANT};