Revert "Dart2js support for custom element lifecycle events"

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index ed225d751182551b01af8ace89a8bcd438042413..25a0c3242ad73671264ca3ca6459ec665edee2f3 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -9710,20 +9710,6 @@ abstract class Element extends Node implements ParentNode, ChildNode {
   @Experimental()
   void created() {}
 
-  /**
-   * Called by the DOM when this element has been inserted into the live
-   * document.
-   */
-  @Experimental()
-  void enteredView() {}
-
-  /**
-   * Called by the DOM when this element has been removed from the live
-   * document.
-   */
-  @Experimental()
-  void leftView() {}
-
   // Hooks to support custom WebComponents.
 
   Element _xtag;