Revert D25507480: [quant][docs] Add fx graph mode quantization to quantization docs
Test Plan: revert-hammer
Differential Revision:
D25507480 (https://github.com/pytorch/pytorch/commit/7729581414962ac0a23ebd269f165f6a877490ae)
Original commit changeset: 9e9e4b5fef97
fbshipit-source-id: fdb08d824209b97defaba2e207d1a914575a6ae7
