Merge "Remove deprecated BOARD_BUILD_SYSTEM_ROOT_IMAGE" am: 47ba5c4713

Original change: https://android-review.googlesource.com/c/device/generic/trusty/+/2175784

Change-Id: Ia5412392e805e475f36aa9ec1955b23b9bb1bf1e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>