Revert "dart2js cps: Maintain parent pointers instead of recomputing them."

pkg/compiler/lib/src/cps_ir/cps_fragment.dart

Index: pkg/compiler/lib/src/cps_ir/cps_fragment.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
index cecad3191c8bbc8f295d11f3cc67b0f8b5d9a3c6..4a1f34056156fdb184f01b250f4e70d3856e78cf 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
@@ -83,7 +83,6 @@ class CpsFragment {
     }
     if (context != null) {
       context.body = node;
-      node.parent = context;
     }
     context = null;
   }
@@ -298,19 +297,4 @@ class CpsFragment {
     put(let);
     context = let;
   }
-
-  void insertBelow(InteriorNode node) {
-    assert(isOpen);
-    if (isEmpty) return;
-    Expression child = node.body;
-    node.body = root;
-    root.parent = node;
-    context.body = child;
-    child.parent = context;
-    root = context = null;
-  }
-
-  void insertAbove(InteriorExpression node) {
-    insertBelow(node.parent);
-  }
 }