Remove admin_style_v2 description

Partially reverts 9a1b1498bf

lib/open_food_network/feature_toggle.rb

@@ -11,9 +11,6 @@ module OpenFoodNetwork
     # We way move this to a YAML file when it becomes too awkward.
     # **WARNING:** Features not in this list will be removed.
     CURRENT_FEATURES = {
-      "admin_style_v2" => <<~DESC,
-        Change some colour and layout in the backend to a newer version.
-      DESC
       "api_reports" => <<~DESC,
         An API endpoint for reports at
         <code>/api/v0/reports/:report_type(/:report_subtype)</code>