[Core] Deprecating block manager v1 and make block manager v2 default (#8704)

Removing the block manager v1. This is the initial piece of prefix-caching-centric design. In order to achieve prefix-caching-centric design, we need to simplify the code path so that we only use v2 block manager (which has much higher performance on prefix caching).

vllm/envs.py

@@ -64,7 +64,6 @@ if TYPE_CHECKING:
     VLLM_USE_TRITON_AWQ: bool = False
     VLLM_ALLOW_RUNTIME_LORA_UPDATING: bool = False
     VLLM_SKIP_P2P_CHECK: bool = False
-    VLLM_ALLOW_DEPRECATED_BLOCK_MANAGER_V1: bool = False
     VLLM_TORCH_COMPILE_LEVEL: int = 0
     VLLM_DISABLED_KERNELS: List[str] = []
 
@@ -427,11 +426,6 @@ environment_variables: Dict[str, Callable[[], Any]] = {
     "VLLM_SKIP_P2P_CHECK":
     lambda: os.getenv("VLLM_SKIP_P2P_CHECK", "0") == "1",
 
-    # If set, allowing the use of deprecated block manager V1
-    "VLLM_ALLOW_DEPRECATED_BLOCK_MANAGER_V1":
-    lambda: os.environ.get("VLLM_ALLOW_DEPRECATED_BLOCK_MANAGER_V1", "0"
-                           ) == "1",
-
     # List of quantization kernels that should be disabled, used for testing
     # and performance comparisons. Currently only affects MPLinearKernel
     # selection