Remove stale layer_transfer_counter prefetch guards (port from e293d4a39 fix #3)

CpSharedKVMlaPrefetcher.create and CpSharedKVIndexPrefetcher.create
returned None whenever ``token_to_kv_pool.layer_transfer_counter`` was
set, which permanently disables NSA indexer prefetch whenever HiCache
is active — even when no H2D transfer is in progress.

The guard is unnecessary: buffer getters synchronize via wait_until(),
and the prefetcher's stream calls wait_stream(current_stream) before
materialization. Removing it restores intended prefetch parallelism
under HiCache + NSA.

Only fix #3 of e293d4a39 is portable to this branch — fixes #1 (SHM
timeout) and #2 (SHM exception safety) target shm_allreduce.py and the
batched-CP coordination path in hiradix_cache.py, neither of which
exists here.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

python/sglang/srt/layers/attention/nsa/cp_shared_kv_prefetch.py

@@ -178,9 +178,6 @@ class CpSharedKVMlaPrefetcher:
         if token_to_kv_pool is None:
             _prefetch_log("create_skip reason=missing_token_to_kv_pool")
             return None
-        if getattr(token_to_kv_pool, "layer_transfer_counter", None) is not None:
-            _prefetch_log("create_skip reason=layer_transfer_active")
-            return None
 
         layout = getattr(forward_batch, "cp_shared_kv_layout", None)
         if layout is None:
@@ -705,12 +702,6 @@ class CpSharedKVIndexPrefetcher:
                 "forward batch has no token_to_kv_pool.",
             )
             return None
-        if getattr(token_to_kv_pool, "layer_transfer_counter", None) is not None:
-            _index_prefetch_fallback_log(
-                "layer_transfer_active",
-                "layer transfer is active.",
-            )
-            return None
 
         layout = getattr(forward_batch, "cp_shared_kv_layout", None)
         if layout is None: