Revert METADATA to newer format am: 4cdc1ce888 am: a34dfc5661 am: b7a0eb81c8

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/base64/+/2856668

Change-Id: Idd76805c0a82cd1fea31256e721a6a9ebca86ce4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>