libc++fs is part of libc++ now. am: 160fbc4a97 am: ffb5229924

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3116324

Change-Id: I546d4169a55d41ebb9f6e23a7b1b8b601f96c86e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>