Remove stale files from lib/html/src.

lib/html/src/WheelEventWrappingImplementation.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-class WheelEventWrappingImplementation extends UIEventWrappingImplementation implements WheelEvent {
-  WheelEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
-
-  factory WheelEventWrappingImplementation(int deltaX, int deltaY, Window view,
-      int screenX, int screenY, int clientX, int clientY, [bool ctrlKey = false,
-      bool altKey = false, bool shiftKey = false, bool metaKey = false]) {
-    final e = dom.document.createEvent("WheelEvent");
-    e.initWebKitWheelEvent(deltaX, deltaY, LevelDom.unwrap(view), screenX, screenY,
-        clientX, clientY, ctrlKey, altKey, shiftKey, metaKey);
-    return LevelDom.wrapWheelEvent(e);
-  }
-
-  bool get altKey() => _ptr.altKey;
-
-  int get clientX() => _ptr.clientX;
-
-  int get clientY() => _ptr.clientY;
-
-  bool get ctrlKey() => _ptr.ctrlKey;
-
-  bool get metaKey() => _ptr.metaKey;
-
-  int get offsetX() => _ptr.offsetX;
-
-  int get offsetY() => _ptr.offsetY;
-
-  int get screenX() => _ptr.screenX;
-
-  int get screenY() => _ptr.screenY;
-
-  bool get shiftKey() => _ptr.shiftKey;
-
-  int get wheelDelta() => _ptr.wheelDelta;
-
-  int get wheelDeltaX() => _ptr.wheelDeltaX;
-
-  int get wheelDeltaY() => _ptr.wheelDeltaY;
-
-  int get x() => _ptr.x;
-
-  int get y() => _ptr.y;
-}