Revert D24486972: [quant][graphmode][fx] Support sigmoid/hardsigmoid/tanh in qat
Test Plan: revert-hammer
Differential Revision:
D24486972 (https://github.com/pytorch/pytorch/commit/e927b62e739cb433bbf19ce56d78e6b4c9da8b70)
Original commit changeset: c9f139bfdd54
fbshipit-source-id: 2a75f5ec93d55a62b40d1cdd49adcf65436058f7
