Setting: remove unused actor in default_fee_type validation

- Docs: Regenerate Cycles server-side enforcement note in membership-fee-architecture.

lib/membership/setting.ex

@@ -160,14 +160,6 @@ defmodule Mv.Membership.Setting do
                  Ash.Changeset.get_attribute(changeset, :default_membership_fee_type_id)
 
                if fee_type_id do
-                 # Actor may be in changeset.context (action context) or validation context
-                 ctx = changeset.context || %{}
-
-                 actor =
-                   get_in(ctx, [:private, :actor]) ||
-                     Map.get(ctx, :actor) ||
-                     (context && Map.get(context, :actor))
-
                  # Check existence only; action is already restricted by policy (e.g. admin).
                  opts = [domain: Mv.MembershipFees, authorize?: false]