libc++fs is now part of libc++. am: 9f219cff94

Original change: https://android-review.googlesource.com/c/device/google/barbet/+/3122871

Change-Id: I3c0a334d7b9ea7f69adc58c1843fb49be67b749a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>