Generate apex_available from c2a instead of a patch am: a4c43fafd2 am: d1bb8b6b84 am: 3d54d6c5d6

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt/+/1689919

Change-Id: Ic378b1094830f1705e41f8bde17992f6e73df703