Remove fx2trt/torch2trt backends (#93822)
These backends have been broken for some time. I tried to get them
running again, but as far as I can tell they are not maintained.
Installing torch_tensorrt downgrades PyTorch to 1.12. If I manually
bypass that downgrade, I get import errors from inside fx2trt. Fixes that
re-add these are welcome, but it might make sense to move these wrappers
to the torch_tensorrt repo once PyTorch 2.0 support is added.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93822
Approved by: https://github.com/frank-wei
