Generate apex_available from c2a instead of a patch am: b5eff22717 am: 131adf326c am: 8e459e84c0 am: b5540afb16

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-io/+/1688786

Change-Id: I45c21ddc5824da3a22115a5c69f7819b1e51d2fc