Remove an unused variable in SoftmaxWithLossOp (#56321)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/56321
Reviewed By: heitorschueroff
Differential Revision: D27854332
Pulled By: bdhirsh
fbshipit-source-id: 1a9dcfdc63412069cee4444a595c3460815d3c6c
