Remove unused slowpath locking method in OptoRuntime

Create JBS on healf of github id miao-zheng

Following methods are declared but no implemeantion and usage.

 // Slow-path Locking and Unlocking
  static void complete_monitor_locking_C(oopDesc* obj, BasicLock* lock, JavaThread* thread);
  static void complete_monitor_unlocking_C(oopDesc* obj, BasicLock* lock, JavaThread* thread);