comment out large test cases for tril(u)_indices (#15959)
Summary:
4GB is still too large and leads to CUDA OOM failures.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15959
Differential Revision: D13635146
Pulled By: mrshenli
fbshipit-source-id: 3dc34a03d6ed65c458839d8fa37cd05bf3bc8106
