android [nfc]: Remove a now-unneeded import

When this was written in Java, the `ReactContext` type was used to
declare a variable, and we don't need it now that the file is in
Kotlin.

Author: chrisbobbe

android/app/src/main/java/com/zulipmobile/notifications/FcmListenerService.kt

@@ -2,7 +2,6 @@ package com.zulipmobile.notifications
 
 import com.google.firebase.messaging.FirebaseMessagingService
 import com.google.firebase.messaging.RemoteMessage
-import com.facebook.react.bridge.ReactContext
 import com.facebook.react.ReactApplication
 
 class FcmListenerService : FirebaseMessagingService() {