[branch-2.1]Reset io limit default value (#39898)

pick #39842

be/src/runtime/workload_management/io_throttle.h

@@ -47,7 +47,7 @@ private:
     std::mutex _mutex;
     std::condition_variable wait_condition;
     int64_t _next_io_time_micros {0};
-    std::atomic<int64_t> _io_bytes_per_second_limit {10485760};
+    std::atomic<int64_t> _io_bytes_per_second_limit {-1};
 
     // bvar monitor
     std::unique_ptr<bvar::Adder<size_t>> _io_adder;