Kernel: Remove obsolete Scheduler::is_valid_tid()

This function was used when processes could die at any point in time.
Now that processes can only die in known spots, we can be sure they
are not holding any locks. This allows much more performant locking.

kernel/kernel/Scheduler.cpp

@@ -378,26 +378,4 @@ namespace Kernel
 		}
 	}
 
-	bool Scheduler::is_valid_tid(pid_t tid)
-	{
-		CriticalScope _;
-
-		if (s_instance == nullptr)
-			return tid == 0;
-
-		for (auto& thread : s_instance->m_active_threads)
-			if (thread.thread->tid() == tid)
-				return true;
-		
-		for (auto& thread : s_instance->m_sleeping_threads)
-			if (thread.thread->tid() == tid)
-				return true;
-
-		for (auto& thread : s_instance->m_blocking_threads)
-			if (thread.thread->tid() == tid)
-				return true;
-
-		return false;
-	}
-
-}
+}

kernel/kernel/SpinLock.cpp

@@ -13,7 +13,7 @@ namespace Kernel
 			{
 				CriticalScope _;
 				ASSERT(m_locker != tid);
-				if (m_locker == -1 || !Scheduler::is_valid_tid(m_locker))
+				if (m_locker == -1)
 				{
 					m_locker = tid;
 					break;
@@ -48,7 +48,7 @@ namespace Kernel
 				m_lock_depth++;
 				break;
 			}
-			if (m_locker == -1 || !Scheduler::is_valid_tid(m_locker))
+			if (m_locker == -1)
 			{
 				m_locker = tid;
 				m_lock_depth = 1;