[DDP] Remove unused initialize_buckets (#59066)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59066
Per title
ghstack-source-id: 130338812
Test Plan: ci
Reviewed By: SciPioneer
Differential Revision: D28734666
fbshipit-source-id: 89ca7f8e625c4068ba0ed9800be2619e469ae515
