Build skyx packages by default

sky/sdk/example/demo_launcher/BUILD.gn

 # 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("//sky/build/sky_app.gni")
 
 sky_app("demo_launcher") {
-  apk_name = "SkyDemo"
   main_dart = "lib/main.dart"
   manifest = "sky.yaml"
 
-  if (enable_skyx) {
+  if (is_android) {
+    apk_name = "SkyDemo"
+
     bundles = [
       "//sky/sdk/example/mine_digger",
       "//sky/sdk/example/rendering:interactive_flex",
       "//sky/sdk/example/stocks",
       "//sky/sdk/example/widgets:sector",
     ]
+
+    deps = [
+      "//sky/sdk/example/demo_launcher/apk:java",
+      "//sky/sdk/example/demo_launcher/apk:resources",
+    ]
   }
-
-  deps = [
-    "//sky/sdk/example/demo_launcher/apk:java",
-    "//sky/sdk/example/demo_launcher/apk:resources",
-  ]
 }