This reverts commit f41b3411da35929b09009e47cb52474389e42874, reversing
changes made to e33d8d96212f3e337a6660f1eb1118bffc945bf5.
This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.
This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640
Most of the remaining widget examples are actually manual tests. This patch
moves them into //dev/manual_tests. A couple are examples of using services,
which I've moved to //examples/layers/services. The remainder are out-dated and
are removed by this patch.