Remove unused code in delta_generator am: ed9b208e12 am: 1ac579cd98

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

Change-Id: Ie7088e89ab85d2934325d70d93f613e1bb1777d5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>