Apply Threadpool changes

Author: lowener

src/index/cagra/cagra.cu

@@ -22,13 +22,7 @@ static constexpr uint32_t cuda_concurrent_size = 16;
 
 namespace knowhere {
 
-static std::shared_ptr<ThreadPool>
-GlobalThreadPoolRaft() {
-    static std::shared_ptr<ThreadPool> pool = std::make_shared<ThreadPool>(cuda_concurrent_size);
-    return pool;
-}
-
 KNOWHERE_REGISTER_GLOBAL(GPU_RAFT_CAGRA, [](const Object& object) {
-    return Index<IndexNodeThreadPoolWrapper>::Create(std::make_unique<CagraIndexNode>(object), GlobalThreadPoolRaft());
+    return Index<IndexNodeThreadPoolWrapper>::Create(std::make_unique<CagraIndexNode>(object), cuda_concurrent_size);
 });
 }  // namespace knowhere