Remove assertion that substitutions are erased. It'd be nice if they

always were but it's dang annoying to weed out all the places that
fail to meet the assertion, and it doesn't really hurt things if we don't
always get it right.

src/librustc_trans/trans/monomorphize.rs

@@ -300,8 +300,6 @@ pub fn apply_param_substs<'tcx,T>(tcx: &ty::ctxt<'tcx>,
                                   -> T
     where T : TypeFoldable<'tcx> + Repr<'tcx> + HasProjectionTypes + Clone
 {
-    assert!(param_substs.regions.is_erased());
-
     let substituted = value.subst(tcx, param_substs);
     normalize_associated_type(tcx, &substituted)
 }