DefaultCaptchaService#onUserCreated can be slow when synchronising large LDAP directories

Currently com.atlassian.stash.internal.auth.DefaultCaptchaService#onUserCreated resets the CAPTCHA failed authentication attempts when a user is created. This event is a synchronous event and happens inside transactions which occur during LDAP synchronisation which in turn triggers slow isDirty checks in hibernate.

It is recommended that we remove this event listener as it provides little value in a scenario which is an edge case