improve experience of USB YubiKeys on Android

Author: AdamVe

android/app/src/main/kotlin/com/yubico/authenticator/MainActivity.kt

@@ -167,6 +167,7 @@ class MainActivity : FlutterFragmentActivity() {
 
         appPreferences.unregisterListener(sharedPreferencesListener)
 
+        stopUsbDiscovery()
         stopNfcDiscovery()
         if (!appPreferences.openAppOnUsb) {
             enableAliasMainActivityComponent(false)