The easiest way is to create a template override for the K2 User module and simply remove that link. OR if you don't use comments in K2 at all, disable them in K2's parameters/settings and that link will hide.

For more info on K2 template overrides, have a look at this guide please: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates?upd