Merge "Remove deprecated BOARD_BUILD_SYSTEM_ROOT_IMAGE" am: 47ba5c4713 am: c9b1afa100

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

Change-Id: I03b911213ace493e4eab4a7c349d8c1480a875f0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>