Make implemented DeathRecipient in A11yServiceConnection clear

binderDied() is a method in the interface DeathRecipient. Make it clear
we're overriding

Bug: n/a
Test: builds
Change-Id: I31e3107489036fe23605e06d71addc834d038f63

services/accessibility/java/com/android/server/accessibility/AccessibilityServiceConnection.java

@@ -368,6 +368,7 @@ class AccessibilityServiceConnection extends AbstractAccessibilityServiceConnect
         }
     }
 
+    @Override
     public void binderDied() {
         synchronized (mLock) {
             // It is possible that this service's package was force stopped during