Delete untested, broken Model2LSTM (#2968)

src/transformers/modeling_encoder_decoder.py

@@ -18,7 +18,6 @@
 import logging
 import os
 
-import torch
 from torch import nn
 
 from .modeling_auto import AutoModel, AutoModelWithLMHead
@@ -294,21 +293,3 @@ class Model2Model(PreTrainedEncoderDecoder):
         )
 
         return model
-
-
-class Model2LSTM(PreTrainedEncoderDecoder):
-    @classmethod
-    def from_pretrained(cls, *args, **kwargs):
-        if kwargs.get("decoder_model", None) is None:
-            # We will create a randomly initilized LSTM model as decoder
-            if "decoder_config" not in kwargs:
-                raise ValueError(
-                    "To load an LSTM in Encoder-Decoder model, please supply either: "
-                    "    - a torch.nn.LSTM model as `decoder_model` parameter (`decoder_model=lstm_model`), or"
-                    "    - a dictionary of configuration parameters that will be used to initialize a"
-                    "      torch.nn.LSTM model as `decoder_config` keyword argument. "
-                    "      E.g. `decoder_config={'input_size': 768, 'hidden_size': 768, 'num_layers': 2}`"
-                )
-            kwargs["decoder_model"] = torch.nn.LSTM(kwargs.pop("decoder_config"))
-        model = super().from_pretrained(*args, **kwargs)
-        return model