Changed delta_generator to make use of --max_threads am: cbe8e633f2 am: 607027dea6 am: 41c5f6108a

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2562931

Change-Id: Id1889d194735822c9ae1b87c2ce57cd52842bc39
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>