update build_android.sh to not build host protoc for libtorch (#25896)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25896
Similar change as PR #25822.
Test Plan:
- Updated CI to use the new script.
- Will check pytorch android CI output to make sure it builds libtorch
instead of libcaffe2.
Reviewed By: dreiss
Differential Revision: D17279722
Pulled By: ljk53
fbshipit-source-id: 93abcef0dfb93df197fabff29e53d71db5674255
