pytorch

671160a9 - Revert D23557576: Revert D23519521: [dper3] replace LengthsGather lowlevel module's PT implemetnatio to use caffe2 op

Revert D23557576: Revert D23519521: [dper3] replace LengthsGather lowlevel module's PT implemetnatio to use caffe2 op Test Plan: revert-hammer Differential Revision: D23557576 Original commit changeset: 33631299eabe fbshipit-source-id: 704d36a16346f047b30e2da8be882062135f8617