Upgrade rust/crates/structopt-derive to 0.4.15 am: 7081b4a371 am: 2aef36ce18

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt-derive/+/1791009

Change-Id: Ib0bc5159e70ca08dbd001ba600f9477cf1228d7d