Check named buffers in emitter, for non-persistent buffers (#1865)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1865

Non-persistent buffers should not show up in the state dict, after D53340041.
See [comments here](https://github.com/pytorch/pytorch/pull/118969/files#diff-4a060a24e1f81389eab7390d434dddf919af50aa8fda6cbd81e182a53bd9328eR2917-R2922).

freqs_cos and freqs_sin are [non-persistent](https://www.internalfb.com/code/fbsource/[656b0c837314]/fbcode/executorch/examples/models/llama2/model.py?lines=376), causing export issues like P1181876388. Thanks larryliu0820 for the pointers!

Reviewed By: larryliu0820

Differential Revision: D53500886

fbshipit-source-id: 23043ac1f315fee2fc031fd40d9e867cf5d14061