Revert "rustc: Create def IDs for region parameters"

This reverts commit 0d4cb75949.

src/rustc/syntax/ast_util.rs

@@ -39,8 +39,7 @@ fn def_id_of_def(d: def) -> def_id {
       def_native_mod(id) | def_const(id) |
       def_variant(_, id) | def_ty(id) | def_ty_param(id, _) |
       def_use(id) |
-      def_class(id) | def_class_field(_, id) | def_class_method(_, id) |
-      def_region_param(id) { id }
+      def_class(id) | def_class_field(_, id) | def_class_method(_, id) { id }
 
       def_arg(id, _) | def_local(id, _) | def_self(id) |
       def_upvar(id, _, _) | def_binding(id) {