Add fx2trt pass for removing duplicate output args (#64433)

Add fx2trt pass for removing duplicate output args (#64433)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64433

Fx2TRT does not support duplicate nodes in the output args tuple.

This pass removes duplicate output args from the target subnets and fixes their uses in the top level module where the subnets are called. This pass must be called after acc split on the top-level net and subsequent calls to the acc trace on the subnets.

This pass will change both the subnets and top level module.

Test Plan:
Run:

```
buck run mode/opt -c python.package_style=inplace //caffe2/torch/fb/fx2trt/tests/passes/:test_remove_duplicate_output_args

```

Reviewed By: 842974287

Differential Revision: D30468409

fbshipit-source-id: b4d91b76ab5d8a5275d68dd48d1327a44c22568e