Kernel: Lock::unlock_if_locked() should never donate to holder.

Since we're not interested in taking the lock if it's already held,
there's no need to donate the remainder of our time slice to the holder.

Kernel/Lock.h

@@ -113,7 +113,6 @@ inline bool Lock::unlock_if_locked()
             m_lock = 0;
             return true;
         }
-        Scheduler::donate_to(m_holder, m_name);
     }
 }