Revert D26249330: [Gradient Compression] Add a documentation page for DDP communication hooks
Test Plan: revert-hammer
Differential Revision:
D26249330 (https://github.com/pytorch/pytorch/commit/e62aabac43720b42f89cbe0ebd76fa22099ac698)
Original commit changeset: ab973390ddb7
fbshipit-source-id: d508daed76219e7ca588cf7fb38aeaaffc61acfd
