Remove unused argument "destId" in addSendRpcBackward (#31207)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31207
Cleanup after #30914.
In #30914, `autogradContext->addKnownWorkerId(dst);` was moved out of `addSendRpcBackward()`.
So `addSendRpcBackward()` does not need `dstId` as it's argument anymore.
ghstack-source-id: 95509218
Test Plan:
# Unit tests
```
buck test mode/dev-nosan //caffe2/test:dist_autograd_fork -- test_context_cleanup_tensor_no_grad
```
Differential Revision: D5742365
fbshipit-source-id: accd041a594ec18d369231f5590289828d87baa7
