Fixing minor nit

Author: ankitaj224

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -291,9 +291,7 @@ public synchronized FidListenerHandle registerFidListener(@NonNull FidListener l
       @Override
       public void unregister() {
         synchronized (FirebaseInstallations.this) {
-          if (fidListeners.contains(listener)) {
-            fidListeners.remove(listener);
-          }
+          fidListeners.remove(listener);
         }
       }
     };