Fix Falcon weight mapping for H2O.ai checkpoints (#953)

# What does this PR do?
During the safetensor conversion, duplicate weights are removed.
However, which of the duplicates gets removed, differs per checkpoint.
In some, like `h2oai/h2ogpt-oig-oasst1-falcon-40b`, the weight
`transformer.word_embeddings.weightSafetensor` gets removed. In others,
`lm_head.weight` gets removed. Long story long, we need to support both.

Originally, f0181436 mapped `lm_head` to `word_embeddings`. Then ac736fd8
switched this around. This commit merges them and allows for both.

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Did you read the [contributor
guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
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[forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes?
Here are the
[documentation
guidelines](https://github.com/huggingface/transformers/tree/main/docs),
and
[here are tips on formatting
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- [ ] Did you write any new necessary tests?


## Who can review?

@Narsil, you wrote both commits I referenced in this PR. I think you'll
understand this change :)

server/text_generation_server/models/flash_rw.py

@@ -54,7 +54,10 @@ class FlashRWSharded(FlashCausalLM):
             device,
             dtype,
             process_group=self.process_group,
-            aliases={"lm_head.weight": ["transformer.word_embeddings.weight"]},
+            aliases={
+                "lm_head.weight": ["transformer.word_embeddings.weight"],
+                "transformer.word_embeddings.weight": ["lm_head.weight"],
+            },
         )
 
         config.quantize = quantize