avoid null value error

Author: Niall Brennan

src/main/java/com/segment/analytics/android/integrations/firebase/FirebaseIntegration.java

@@ -26,7 +26,6 @@
 
 import static com.segment.analytics.internal.Utils.hasPermission;
 import static com.segment.analytics.internal.Utils.isNullOrEmpty;
-import static java.util.Objects.isNull;
 
 /**
  * Google Analytics for Firebase is a free app measurement solution that provides insight on app