Misc clean up; Remove the support of jump forward (#4032)

python/sglang/srt/layers/attention/flashinfer_mla_backend.py

@@ -15,7 +15,7 @@ from typing import TYPE_CHECKING, Optional, Union
 import torch
 
 from sglang.global_config import global_config
-from sglang.srt.layers.attention import AttentionBackend
+from sglang.srt.layers.attention.base_attn_backend import AttentionBackend
 from sglang.srt.layers.attention.flashinfer_backend import (
     create_flashinfer_kv_indices_triton,
 )
@@ -34,7 +34,6 @@ if is_flashinfer_available():
         BatchMLAPagedAttentionWrapper,
         BatchPrefillWithRaggedKVCacheWrapper,
     )
-    from flashinfer.cascade import merge_state
 
 
 @dataclass