Revert D28922548: [Gradient Compression] Apply division first to avoid overflow
Test Plan: revert-hammer
Differential Revision:
D28922548 (https://github.com/pytorch/pytorch/commit/459270ac01f1bfcbeaffb20f1c94622561af94e0)
Original commit changeset: 442bd3cc7a35
fbshipit-source-id: 7e4361b4eb283cdb21f15a36d6eebf558dd7386f
