[JIT] Remove dead stores in loopnest.cpp (#40626)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/40626
Test Plan: Continuous integration.
Reviewed By: ZolotukhinM
Differential Revision: D22259586
fbshipit-source-id: 447accb5b94392f0b5e4c27956a34403bb0d1ea8
