Merge "Revert "Mark BOARD_BUILD_SYSTEM_ROOT_IMAGE as KATI_obsolete_var"" am:...

Merge "Revert "Mark BOARD_BUILD_SYSTEM_ROOT_IMAGE as KATI_obsolete_var"" am: 3946ea03 am: 6959dea6

Original change: https://android-review.googlesource.com/c/platform/build/+/2267723



Change-Id: I7d097e2c3a8315f73c054c977fab66a7ac912850
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>