Remove unused code in delta_generator am: ed9b208e12

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2605631

Change-Id: I0f4cd77cc1f3662c0e5feab7d012eaadc40b15cb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>