Remove V2 Deprecation banner on about:tor for desktop

As per feedback from the community described here: tor-browser#40523 (comment 2743842), let's remove the V2 Deprecation banner from about:tor.

This ticket concerns the banner on about:tor only, and does not include any changes to the V2 onion address warnings, which will be detailed here if required: tor-browser#40523 (closed).