Revert D23583017: move rebuild buckets from end of first iteration to beginning of second iteration
Test Plan: revert-hammer
Differential Revision:
D23583017 (https://github.com/pytorch/pytorch/commit/f5d231d5933e0ca8feb59f9fe76913d8aa720457)
Original commit changeset: ef67f79437a8
fbshipit-source-id: fd914b7565aba6a5574a32b31403525abb80ff07
