DNS User filter isn't clear after the import #2972

DNS User filter isn't clear after the import a JSON file with the settings where DNS User filter is empty.

Preconditions:

Some example rule like google.com 0.0.0.0 should be added to the DNS User filter and JSON file (example.json) with default settings must be prepared.

Steps to reproduce

1. Enable AdGuard, check that example rule (google.com 0.0.0.0) is added ot the DNS User filter
2. Go to Settings - Import settings - example.json

Expected behavior

DNS User filter should be empty

Actual behavior

DNS User filter contains obsolete rule (before importing)

Customer ID

Your environment

• Adguard version:
• Adguard filtering mode: (e.g. Local VPN / HTTP Proxy (Auto/Manual))
• Device model: (e.g. Google Pixel)
• Operating system and version: (e.g. Android 7.1.2)
• Root access: (e.g. Yes / No)
• Any other apps that can start VPN / Antiviruses / Cleaners etc. installed?: