[small][batch invariance] Rename the env and internal flags to simplify usage (#26855)

Signed-off-by: Bram Wasti <bwasti@meta.com>

vllm/model_executor/layers/layernorm.py

@@ -10,7 +10,7 @@ import vllm.envs as envs
 from vllm.model_executor.custom_op import CustomOp
 from vllm.model_executor.layers.batch_invariant import (
     rms_norm_batch_invariant,
-    vllm_kernel_override_batch_invariant,
+    vllm_is_batch_invariant,
 )
 from vllm.platforms import current_platform
 from vllm.utils import direct_register_custom_op
@@ -25,7 +25,7 @@ def rms_norm(
 ) -> torch.Tensor:
     from vllm import _custom_ops as ops
 
-    if vllm_kernel_override_batch_invariant():
+    if vllm_is_batch_invariant():
         return rms_norm_batch_invariant(x, weight, variance_epsilon)
     out = torch.empty_like(x)
     ops.rms_norm(
@@ -45,7 +45,7 @@ def fused_add_rms_norm(
 ) -> tuple[torch.Tensor, torch.Tensor]:
     from vllm import _custom_ops as ops
 
-    if vllm_kernel_override_batch_invariant():
+    if vllm_is_batch_invariant():
         return rms_norm_batch_invariant(
             x + residual, weight, variance_epsilon
         ), x + residual