[PyTorch] Fix flatbuffer build error on Android (#74518)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74518
This PR consists the following changes:
* Get rid of some unused variables, to workaround `-Werror, -Wunused-variables`.
* Use Android version of `align_alloc()`.
Test Plan: Tested Android build
Reviewed By: iseeyuan
Differential Revision: D35037344
fbshipit-source-id: f0951a9b21dad723770722c72abc2e3c767aa777
(cherry picked from commit 421af7639f4629d95aa3331d309b09d264a63f1e)
