Remove lock of getLockTaskModeState

The state field is declared as volatile. And the field is always
written on display thread without lock. So it is unnecessary to
lock the getter method.

Bug: 173467481
Test: CtsWindowManagerDeviceTestCases
Change-Id: I6324f6745fd849438b7b0d326bd63bd2d0580421

services/core/java/com/android/server/wm/ActivityTaskManagerService.java

@@ -2538,9 +2538,7 @@ public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
 
     @Override
     public int getLockTaskModeState() {
-        synchronized (mGlobalLock) {
-            return getLockTaskController().getLockTaskModeState();
-        }
+        return getLockTaskController().getLockTaskModeState();
     }
 
     @Override