[shardformer]delete xformers (#5859)

* delete xformers

* fix

* fix

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

colossalai/shardformer/policies/bert.py

@@ -11,7 +11,6 @@ import colossalai.shardformer.layer as col_nn
 from ..modeling.bert import (
     BertPipelineForwards,
     bert_sequence_parallel_forward_fn,
-    get_bert_flash_attention_forward,
     get_jit_fused_bert_intermediate_forward,
     get_jit_fused_bert_output_forward,
     get_jit_fused_bert_self_output_forward,
@@ -49,7 +48,6 @@ class BertPolicy(Policy):
             BertLayer,
             BertModel,
             BertOutput,
-            BertSelfAttention,
             BertSelfOutput,
         )
 
@@ -218,16 +216,6 @@ class BertPolicy(Policy):
             target_key=BertEmbeddings,
         )
 
-        # use flash attention
-        if self.shard_config.enable_flash_attention:
-            self.append_or_create_method_replacement(
-                description={
-                    "forward": get_bert_flash_attention_forward(),
-                },
-                policy=policy,
-                target_key=BertSelfAttention,
-            )
-
         # use jit operator
         if self.shard_config.enable_jit_fused:
             self.append_or_create_method_replacement(