Revert D27708346: generate xla codegen in-tree
Test Plan: revert-hammer
Differential Revision:
D27708346 (https://github.com/pytorch/pytorch/commit/51d0212d0f041efd3cea84f715a835146f9ad985)
Original commit changeset: 2289edd641f3
fbshipit-source-id: 86711c07db19833b9e772c558e12accba1432499
