dart2js: fix typo in incremental compilation fix.

pkg/dart2js_incremental/lib/library_updater.dart

Index: pkg/dart2js_incremental/lib/library_updater.dart
diff --git a/pkg/dart2js_incremental/lib/library_updater.dart b/pkg/dart2js_incremental/lib/library_updater.dart
index f70f3a023142af70c671baa04da1fb7768ca0216..f63852f6d72130b1f5a27cbe1fe91579b1b15340 100644
--- a/pkg/dart2js_incremental/lib/library_updater.dart
+++ b/pkg/dart2js_incremental/lib/library_updater.dart
@@ -1258,9 +1258,9 @@ class RemovedFieldUpdate extends RemovalUpdate with JsFeatures {
     }
 
     updates.add(
-        js.statement('delete #.prototype.#', [prototypeAccess, getterName]));
+        js.statement('delete #.#', [prototypeAccess, getterName]));
     updates.add(
-        js.statement('delete #.prototype.#', [prototypeAccess, setterName]));
+        js.statement('delete #.#', [prototypeAccess, setterName]));
   }
 }