Fix pthreadpool guard test (#58977)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58977
* Test was flaky as part of it ran async
* Remove async part to test only the functionality added
Test Plan:
regular test:
`buck test mode/dev //caffe2/aten:test_thread_pool_guard -- --exact 'caffe2/aten:test_thread_pool_guard - TestThreadPoolGuard.TestRunWithGuard' --run-disabled`
stress test:
`buck test mode/dev //caffe2/aten:test_thread_pool_guard -- --exact 'caffe2/aten:test_thread_pool_guard - TestThreadPoolGuard.TestRunWithGuard' --run-disabled --jobs 18 --stress-runs 10 --record-results`
Reviewed By: kimishpatel
Differential Revision: D28703064
fbshipit-source-id: be19da3f42f44288afc726bdb2f40342eee26e01
