Remove ContextClass that is not needed since we're using Vectors

pkg/kernel/lib/transformations/closure/context.dart

Index: pkg/kernel/lib/transformations/closure/context.dart
diff --git a/pkg/kernel/lib/transformations/closure/context.dart b/pkg/kernel/lib/transformations/closure/context.dart
index 6425bb680eae54647dafc85d07e89989cb3d4580..672245f762a5b95e3550dc677f05d9f822192731 100644
--- a/pkg/kernel/lib/transformations/closure/context.dart
+++ b/pkg/kernel/lib/transformations/closure/context.dart
@@ -116,8 +116,6 @@ class LocalContext extends Context {
       this.converter, this.parent, this.self, this.vectorCreation);
 
   factory LocalContext(ClosureConverter converter, Context parent) {
-    Class contextClass = converter.contextClass;
-    assert(contextClass.constructors.length == 1);
     converter.rewriter.insertContextDeclaration(parent.expression);
 
     return new LocalContext._internal(