title: [React-Native-Firebase]How can i remove onMessage exist event?
body: <p>I declare a onMessage function with do something. But when i navigate to another screen and want to remove FCM.onMessage() in ComponentWillUnmount(). How can i remove that?</p>
  
  <pre><code>const rnfirebase = RNFirebase.initializeApp()
  
  export const FCM = rnfirebase.messaging()
  
  ComponentDidMount(){
      FCM.onMessage((notif)=&gt;{
  
          //Do something
  
      })
  
  }
  ComponentWillUnmount(){
      //I want to remove here
  
  }
  </code></pre>