Revert^2 "gs101: re-enable prebuilt boot.img/boot-user.img usage"

This reverts commit 48a5fe4304e3c5720f468d6b9147ca36bbe9eb4e.

Reason for revert:
Re-enable gs101 prebuilt boot image usage.
All necessary prerequisites have been merged:
cl/399995993, ag/15953678, ag/15953343, ag/15953037, ag/15953719

Bug: 201469630
Bug: 201476061
Change-Id: Idb46a74e7830a274c45fee1f43a52dbcd7e96ca4
1 file changed