Remove AdGuard DNS filter from the FiltersRegistry

[ameshkov]

Prerequisites

• [X] I checked the documentation and understood it;
• [X] I checked to make sure that this issue has not already been filed;

Problem description

We now have a separate HostlistsRegistry and all AdGuard products have their own DNS filtering modules and blocklists.

There's no need to keep AdGuard DNS filter here anymore.

Proposed solution

I suggest marking it as obsolete so that the programs stopped showing it on the filters screen and removed it from the filters meta.

Before doing it, we'll need to check if this change can cause any issues with the old versions so don't merge until the check is done.

Additional information

No response

[slavaleleka]

few kb articles should be updated after it:

• https://github.com/AdguardTeam/KnowledgeBase/blob/master/docs/general/ad-filtering/adguard-filters.md?plain=1#L38
• https://github.com/AdguardTeam/KnowledgeBase/blob/master/docs/adguard-for-ios/solving-problems/system-wide-filtering.md?plain=1#L45