Cleaning up unused child account info fetcher.

The fetcher is only used in Android now, and its usage has been
protected with Android OS macros. For information on how a child
account is detected on Chrome OS, refer to the DD: goo.gl/MhFXdo.

Bug: 791513
Change-Id: I24acf6eed723087cbb44e93cec93ceac4bf1f2f6
Reviewed-on: https://chromium-review.googlesource.com/c/1391306
Commit-Queue: Luciana Maroun <maroun@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621557}
12 files changed