[export] Remove torch._export.export (#119095)
XLA changes: https://github.com/pytorch/xla/pull/6486
Test Plan: CI
Differential Revision: D53316196
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119095
Approved by: https://github.com/ydwu4, https://github.com/zhxchen17, https://github.com/tugsbayasgalan, https://github.com/avikchaudhuri, https://github.com/jerryzh168
