[carp_context_package] Update documentation after change from carp_background_location to location

[MadsVSChristensen]

Release 0.30.1 changed background location package from carp_background_location to location but the documentation still says to change the AppDelegate.swift to import old plugin dependency background_locator.

This causes the following error, as background_locator is no longer part of the project:

 .../ios/Runner/AppDelegate.swift:18:8: error: no such module 'background_locator'
    import background_locator

AppDelegate.swift can be reversed back to:

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

[bardram]

Fixed as part of release 0.31.0.