searchable: refactor searchable_includes.

Pass searchable associations directly to search_attributes instead of
defining them separately in searchable_includes.

app/models/ban.rb

@@ -20,7 +20,7 @@ class Ban < ApplicationRecord
   end
 
   def self.search(params)
-    q = search_attributes(params, :id, :created_at, :updated_at, :expires_at, :reason)
+    q = search_attributes(params, :id, :created_at, :updated_at, :expires_at, :reason, :user, :banner)
     q = q.text_attribute_matches(:reason, params[:reason_matches])
 
     q = q.expired if params[:expired].to_s.truthy?
@@ -87,10 +87,6 @@ class Ban < ApplicationRecord
     ModAction.log(%{Unbanned <@#{user_name}>}, :user_unban)
   end
 
-  def self.searchable_includes
-    [:user, :banner]
-  end
-
   def self.available_includes
     [:user, :banner]
   end