Revert "Add batch invariant kernel override for FlashInfer backend [2/n]" (#26220)

vllm/model_executor/layers/batch_invariant.py

@@ -8,12 +8,8 @@ from typing import Any, Union
 
 import torch
 
-import vllm.envs as envs
-from vllm.logger import init_logger
 from vllm.triton_utils import tl, triton
 
-logger = init_logger(__name__)
-
 
 def _matmul_launch_metadata(grid: Callable[..., Any], kernel: Any,
                             args: dict[str, Any]) -> dict[str, Any]:
@@ -561,12 +557,5 @@ def vllm_kernel_override_batch_invariant():
 def init_batch_invariance():
     # this will hit all the csrc overrides as well
     if vllm_kernel_override_batch_invariant():
-        curr_attn_backend = envs.VLLM_ATTENTION_BACKEND
-        supported_backends = ["FLEX_ATTENTION", "FLASHINFER"]
-        if curr_attn_backend not in supported_backends:
-            warning = "Forcibly updating attention backend to" \
-                f" {supported_backends[0]} for batch_invariant. " \
-                f" Supported backends: {supported_backends}."
-            logger.warning_once(warning)
-            os.environ["VLLM_ATTENTION_BACKEND"] = supported_backends[0]
+        os.environ["VLLM_ATTENTION_BACKEND"] = "FLEX_ATTENTION"
         enable_batch_invariant_mode()