Got no permission error, when I was trying to delete form submission

I got no permission error, when I was trying to delete form submission.
Event permission is checked by "in-portal:submissions" section, but
permission (in group permission editing is set on "in-portal:submissions:1"
(1 is associated form id) section.

To fix this I propose to set proper form-based permission section in
FormSubmissionEventHandler::CheckPermission method.