Removes torchtest, expands generic device testing (#26374)
Summary:
- Removes torchtest
- <s>Moves test_torch tests skipped on ROCm to generic device test class</s>
- Creates test_nn generic device test class
Next: adding dtypes to generic device testing framework.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26374
Test Plan: Change is to tests themselves.
Differential Revision: D17442218
Pulled By: mruberry
fbshipit-source-id: d7e4451d09fc9049478b35a7efb8bb580071e8c8
