Revert "Use interceptors for is-checks (version 2)."

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

Index: pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
diff --git a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
index c06046b3cabbb77801c8616058cfc9fc9a77db14..4aa4ba0143343123e83d5326f9752f7e4c5bafaf 100644
--- a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
+++ b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
@@ -571,11 +571,6 @@ class ParentVisitor extends RecursiveVisitor {
   processTypeTest(TypeTest node) {
     node.typeArguments.forEach((Reference ref) => ref.parent = node);
     node.value.parent = node;
-    if (node.interceptor != null) node.interceptor.parent = node;
-  }
-
-  processTypeTestViaFlag(TypeTestViaFlag node) {
-    node.interceptor.parent = node;
   }
 
   processSetMutable(SetMutable node) {