[Android] Make GMSCore proguarding more aggressive

This patch proguards cast more accurately, keeping only the base
and internal packages, instead of including things that we don't
use like gms.cast.games

BUG=272790

Change-Id: Ieb3ac263b586311cd702bb71428e7d488a50e9d3
Reviewed-on: https://chromium-review.googlesource.com/290590
Reviewed-by: Aurimas Liutikas <aurimas@chromium.org>
Commit-Queue: Aurimas Liutikas <aurimas@chromium.org>
Tested-by: Aurimas Liutikas <aurimas@chromium.org>