rustc stage2 bootstrap cleanup: Remove unused imports and bindings.

As a drive-by, fix the prefix used for the emitted message when
`explain_region_and_span` encounters a `DestructionScope`.

Author: pnkfelix

src/librustc/middle/typeck/check/mod.rs

@@ -87,7 +87,7 @@ use middle::{const_eval, def, traits};
 use middle::lang_items::IteratorItem;
 use middle::mem_categorization::{mod, McResult};
 use middle::pat_util::{mod, pat_id_map};
-use middle::region::{mod, CodeExtent};
+use middle::region::{CodeExtent};
 use middle::subst::{mod, Subst, Substs, VecPerParamSpace, ParamSpace};
 use middle::ty::{FnSig, VariantInfo, Polytype};
 use middle::ty::{Disr, ParamTy, ParameterEnvironment};

src/librustc/middle/typeck/check/regionck.rs

@@ -121,7 +121,6 @@ and report an error, and it just seems like more mess in the end.)
 use middle::def;
 use middle::mem_categorization as mc;
 use middle::region::CodeExtent;
-use middle::subst;
 use middle::traits;
 use middle::ty::{ReScope};
 use middle::ty::{mod, Ty};

src/librustc/middle/typeck/check/wf.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 use middle::region;
-use middle::subst;
 use middle::subst::{Subst};
 use middle::traits;
 use middle::ty::{mod, Ty};
@@ -23,7 +22,6 @@ use util::ppaux::Repr;
 use std::collections::HashSet;
 use syntax::ast;
 use syntax::ast_util::{local_def};
-use syntax::attr;
 use syntax::codemap::Span;
 use syntax::visit;
 use syntax::visit::Visitor;

src/librustc/util/ppaux.rs

@@ -89,8 +89,8 @@ pub fn explain_region_and_span(cx: &ctxt, region: ty::Region)
         ReScope(scope @ CodeExtent::Closure(_)) |
         ReScope(scope @ CodeExtent::DestructionScope(_)) => {
         let node_id = scope.node_id();
-        let prefix = if let CodeExtent::DestructionScope(dtor_id) = scope {
-            "destruction scope surrounding"
+        let prefix = if let CodeExtent::DestructionScope(_) = scope {
+            "destruction scope surrounding "
         } else {
             ""
         };
@@ -925,7 +925,7 @@ impl<'tcx> Repr<'tcx> for ty::FreeRegion {
 }
 
 impl<'tcx> Repr<'tcx> for region::CodeExtent {
-    fn repr(&self, tcx: &ctxt) -> String {
+    fn repr(&self, _: &ctxt) -> String {
         match *self {
             region::CodeExtent::Misc(node_id) =>
                 format!("Misc({})", node_id),