Switch mobile targets to flatbuffers_mobile (#82829)
Differential Revision: [D38412635](https://our.internmc.facebook.com/intern/diff/D38412635/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D38412635/)!
Differential Revision: [D38412635](https://our.internmc.facebook.com/intern/diff/D38412635)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82829
Approved by: https://github.com/qihqi
