frontend/android: remove network state receiver

It is redundant (the current network helper already listens for
connectivity changes) and is also deprecated. See
https://developer.android.com/reference/android/net/ConnectivityManager#CONNECTIVITY_ACTION

Author: Beerosagos

frontends/android/BitBoxApp/app/src/main/java/ch/shiftcrypto/bitboxapp/MainActivity.java

@@ -87,14 +87,6 @@ public void onReceive(Context context, Intent intent) {
         }
     };
 
-    private final BroadcastReceiver networkStateReceiver = new BroadcastReceiver() {
-        @Override
-        public void onReceive(Context context, Intent intent) {
-            Mobileserver.usingMobileDataChanged();
-        }
-    };
-
-
     @Override
     public void onConfigurationChanged(Configuration newConfig) {
         int currentNightMode = newConfig.uiMode & Configuration.UI_MODE_NIGHT_MASK;
@@ -327,9 +319,6 @@ protected void onResume() {
                 ContextCompat.RECEIVER_NOT_EXPORTED
         );
 
-        // Listen on changes in the network connection. We are interested in if the user is connected to a mobile data connection.
-        registerReceiver(this.networkStateReceiver, new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
-
         // Trigger connectivity check (as the network may already be unavailable when the app starts).
         networkHelper.checkConnectivity();
 
@@ -342,7 +331,6 @@ protected void onPause() {
         super.onPause();
         Util.log("lifecycle: onPause");
         unregisterReceiver(this.usbStateReceiver);
-        unregisterReceiver(this.networkStateReceiver);
     }
 
     private void handleIntent(Intent intent) {