android [nfc]: Remove some unused imports in NotificationsModule

Looks like these were added unnecessarily in 0f6cf39.

Author: chrisbobbe

android/app/src/main/java/com/zulipmobile/notifications/NotificationsModule.java

@@ -11,12 +11,9 @@
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 import com.facebook.react.bridge.ReactMethod;
 import com.facebook.react.bridge.WritableMap;
-import com.facebook.react.bridge.WritableNativeMap;
 import com.google.android.gms.common.ConnectionResult;
 import com.google.android.gms.common.GoogleApiAvailability;
 import com.google.firebase.iid.FirebaseInstanceId;
-import java.util.HashMap;
-import java.util.Map;
 
 import static com.zulipmobile.notifications.NotificationUiManager.TAG;