This reverts commit 8da4778e.

* Update hello_world to new gradle based build flow

* Update flutter_gallery to gradle based build

* Align hello_services with new gradle based build

* Update platform_services to new gradle based build

* Upgrade stock to gradle based build

* s/sky/flutter/ in Android templates

* update engine.version with a compatible engine version

* replace more SkyActivity references with FlutterActivity

This is needed to update an app's layout when a soft keyboard is shown

rename example apk dirs to android
removed all BUILD.gn files

Not great.  Better than nothing.

@hixie

This is just one of many steps in preparation for turning
fitness into a play-store ready app.

@abarth @collinjackson