rust: Defaulting --size_t-is-usize

We're defaulting to --size_t-is-usize across the repository to keep
things consistent. This updates bindgen users to deal with the new
signatures.

Bug: 193455107
Test: m
Change-Id: Ie0543de803d08db5501e6a1d3a9b3322f7d6fb10
1 file changed