remove _lazy_init() in rebuild full params (#74263)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74263
remove _lazy_init() in rebuild full params, which was introduced in https://github.com/pytorch/pytorch/pull/73300. _lazy_init() synces streams whenever before rebuilding full params. This sync is not needed when BackwardPrefetch.BACKWARD_PRE is enabled.
ghstack-source-id: 151454522
Test Plan: unit tests
Reviewed By: rohan-varma
Differential Revision: D34907823
fbshipit-source-id: c945057569322f8f6c66f50619f525463a03700d
(cherry picked from commit 497ceb37199dfb33af947af83345b6471f29569e)
