remove some use declarations that got added in during rebase

Author: mikeyhew

src/librustc/traits/object_safety.rs

@@ -23,8 +23,7 @@ use hir::def_id::DefId;
 use lint;
 use traits::{self, Obligation, ObligationCause};
 use ty::{self, Ty, TyCtxt, TypeFoldable, Predicate, ToPredicate};
-use ty::subst::{Subst, Substs};
-use ty::util::ExplicitSelf;
+use ty::subst::{Subst};
 use std::borrow::Cow;
 use std::iter::{self};
 use syntax::ast::{self, Name};