Clear registered prediction callbacks on destroy

destroy() removes callbacks from AppPredictionManagerService but not
from mRegisteredCallbacks.

Bug: 149388856
Test: manual
Change-Id: Id08d6b20362486bd1640310c64da35e0382d9b5e

core/java/android/app/prediction/AppPredictor.java

@@ -260,6 +260,7 @@ public final class AppPredictor {
                 Log.e(TAG, "Failed to notify app target event", e);
                 e.rethrowAsRuntimeException();
             }
+            mRegisteredCallbacks.clear();
         } else {
             throw new IllegalStateException("This client has already been destroyed.");
         }