Fix missing current_user on MemberEntity

Move the `current_user` to MemberEntity from the EE module, to fix a
helper that needs it for a permissions check.

app/serializers/member_entity.rb

@@ -63,6 +63,12 @@ class MemberEntity < Grape::Entity
       member.respond_to?(:invited_user_state) ? member.invited_user_state : ""
     end
   end
+
+  private
+
+  def current_user
+    options[:current_user]
+  end
 end
 
 MemberEntity.prepend_mod_with('MemberEntity')

ee/app/serializers/ee/member_entity.rb

@@ -24,10 +24,6 @@ module EE
 
     private
 
-    def current_user
-      options[:current_user]
-    end
-
     def group
       options[:group]
     end