AdGuard protection is not restored after being revoked by another VPN

[ameshkov]

Example of this issue:
#1922

The current approach to restoring protection is flawed. We need to think of an alternative.

[ameshkov]

Resolved in adguard-android/pull-requests/508

Testing instructions

1. Install any other third-party VPN app;
2. Start AdGuard;
3. Start the third-party VPN;
4. Check that AdGuard is paused and the notification text is relevant;
5. Stop the third-party VPN;
6. Wait for 10-15 seconds and ensure that AdGuard restores protection;