Revert D23917034: quant docs: document how to customize qconfigs in eager mode
Test Plan: revert-hammer
Differential Revision:
D23917034 (https://github.com/pytorch/pytorch/commit/7763e1d7b1be5b13394396646cb00a8766b4a626)
Original commit changeset: ccf71ce4300c
fbshipit-source-id: 9ce99e880b4a22e824f4413354a0f3703e7c5c2c
