Rationalize Dart mojo and sky package structure

sky/framework/elements/sky-button.sky

Index: sky/framework/elements/sky-button.sky
diff --git a/sky/framework/elements/sky-button.sky b/sky/framework/elements/sky-button.sky
deleted file mode 100644
index f5ed65446787d0724ed76b39b3119fa0d2e8838d..0000000000000000000000000000000000000000
--- a/sky/framework/elements/sky-button.sky
+++ /dev/null
@@ -1,46 +0,0 @@
-<!--
-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
--->
-<import src="sky-element.sky" />
-<import src="shadow.sky" as="shadow" />
-
-<sky-element attributes="primary:boolean, level:number">
-<template>
-  <style>
-    :host {
-      display: inline-flex;
-      -webkit-user-select: none;
-      justify-content: center;
-      align-items: center;
-      height: 36px;
-      min-width: 64px;
-      padding: 0 8px;
-      margin: 4px;
-      border-radius: 2px;
-    }
-    :host([primary]) {
-      color: white;
-      background-color: #0098f4;
-    }
-  </style>
-  <content />
-</template>
-<script>
-import "dart:sky";
-
-@Tagname('sky-button')
-class SkyButton extends SkyElement {
-  SkyButton() {
-    tabIndex = 0; // Make focusable.
-  }
-
-  void shadowRootReady() {
-    shadow.applyTo(shadowRoot);
-  }
-}
-
-_init(script) => register(script, SkyButton);
-</script>
-</sky-element>