Remove unused `optimizers` variable in test (#70668)
Summary:
In `TestLRScheduler._test()`, an unused variable `optimizers` is created. This PR is a minor refactoring that removes the variable and the loop block that populates the set.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70668
Reviewed By: wenleix
Differential Revision: D33586236
Pulled By: albanD
fbshipit-source-id: cabf870a8221f144df9d3e2f2b564cdc5c255f5a
