Remove vendor_available from cargo2android.json. am: 43a62263d0

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/libloading/+/2834510

Change-Id: I47a180204f25199c4c1994ee29af0b4e50378950
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>