[functorch] Fix dangling impls (#85299)
Our dangling impls were:
- positive_ (the in-place op just never existed)
- unique (something happened to this op, maybe it was renamed)
Test Plan:
- `import functorch; torch._C._dispatch_find_dangling_impls`
- It's difficult to write a test for this because the number of dangling
impls depends on if `test_dispatch` has been run already or not
(test_dispatch adds a dangling impl)
- Can't remove the torchdynamo skip for this yet either
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85299
Approved by: https://github.com/ezyang
