Remove unnecessary ATen/core/EnableNamedTensor.h (#31117)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31117
After this diff, we will have completely removed the named tensor
feature flagging. This means that named tensors are always on and that
there is no mechanism to turn them off. There should be no more follow-up
diffs.
I performed the deletion of the header with
```
find . -type f -print0 | xargs -0 sed -i '/#include
<ATen\/core\/EnableNamedTensor.h>/d'
```
Test Plan: - wait for CI
Differential Revision: D18934952
Pulled By: zou3519
fbshipit-source-id: 253d059074b910fef15bdf885ebf71e0edf5bea5
