Hide API in Android for API that is discouraged as of ICU 57.

This is introduced as public API in Android N, together with the
preferred API introduced by ICU 55, so there is no need to include
it in Android N at all.

https://android-review.googlesource.com/#/c/209387

These methods, introduced in ICU 55, are promoted to stable in ICU 57,
while the methods they replace are demoted to discouraged.

Android does this ahead of time, already in ICU 56, to avoid introducing
an API in Android N that only is to be used for one release.

http://bugs.icu-project.org/trac/ticket/12186
http://bugs.icu-project.org/trac/changeset/38473#file4

Bug: 22023363
Change-Id: Iad787fa3cfcfa765ac3c645cfb56c211e6ffb88e
2 files changed