[TensorExpr] fix warnings (#36167)
Summary:
Fix a bunch of minor warnings in jit/tensorexpr, mostly unused variable & wrong sign comparisons.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36167
Differential Revision: D20905081
Pulled By: nickgg
fbshipit-source-id: 16fe605a86f08596f64e74e9337c59a2581a4d5a
