[Doc] Remove float32 choice from --lora-dtype

[xyang16]

Remove float32 choice from --lora-dtype because float32 is not really supported.

I ran the command below following https://github.com/vllm-project/vllm/blob/main/docs/source/models/lora.rst:

vllm serve meta-llama/Llama-2-7b-hf \
    --enable-lora \
    --lora-modules sql-lora=$HOME/.cache/huggingface/hub/models--yard1--llama-2-7b-sql-lora-test/snapshots/0dfa347e8877a4d4ed19ee56c140fa518470028c/ \
    --lora-dtype float32

Got the error below because of AssertionError: https://github.com/vllm-project/vllm/blob/main/vllm/lora/ops/sgmv_expand.py#L133-L136

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/dist-packages/vllm/worker/model_runner_base.py", line 116, in _wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/worker/model_runner.py", line 1658, in execute_model
    hidden_or_intermediate_states = model_executable(
                                    ^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1553, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1562, in _call_impl
    return forward_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/models/llama.py", line 558, in forward
    model_output = self.model(input_ids, positions, kv_caches,
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1553, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1562, in _call_impl
    return forward_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/models/llama.py", line 338, in forward
    hidden_states = self.get_input_embeddings(input_ids)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/model_executor/models/llama.py", line 323, in get_input_embeddings
    return self.embed_tokens(input_ids)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1553, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/nn/modules/module.py", line 1562, in _call_impl
    return forward_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/lora/layers.py", line 252, in forward
    self.punica_wrapper.add_expand(full_output,
  File "/usr/local/lib/python3.12/dist-packages/vllm/lora/punica.py", line 487, in add_expand
    expand_fun(y, x, w_t_all, add_input)
  File "/usr/local/lib/python3.12/dist-packages/vllm/lora/punica.py", line 399, in expand_prefill
    sgmv_expand(
  File "/usr/local/lib/python3.12/dist-packages/torch/_library/custom_ops.py", line 506, in __call__
    return self._opoverload(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/_ops.py", line 667, in __call__
    return self_._op(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/_library/custom_ops.py", line 494, in adinplaceorview_impl
    return self._opoverload.redispatch(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/_ops.py", line 672, in redispatch
    return self_._handle.redispatch_boxed(keyset, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/_library/custom_ops.py", line 236, in backend_impl
    result = self._backend_fns[device_type](*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/torch/utils/_contextlib.py", line 116, in decorate_context
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/vllm/lora/ops/sgmv_expand.py", line 136, in _sgmv_expand
    assert lora_b_weights.dtype in [
           ^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError

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[DarkLight1337]

Thanks for removing this confusing bit!