dex2oat: Faster class pruning. am: 7a04783947 am: 2ab18d32e8

Original change: https://android-review.googlesource.com/c/platform/art/+/2062287

Change-Id: If2b84cc94d5f6388acee9ccad93eac69ef079710
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>