Remove my private captive portal detection server

URL: https://github.com/pine64-android/device-softwinner/blob/master/tulip-p1/overlay/frameworks/base/packages/SettingsProvider/res/values/defaults.xml

This server is set for my personal use, but I really don't know why it generates TBs of traffic, I will shut down this server at 2020, please replace it to avoid service interruption.

@jonsmirl 