update_engine: remove unused header am: ffae5016ab

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3297876

Change-Id: I4dd7600a0160bf4d18db73fadae4f16f0ee05a20
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>