core: change required permissions for removing template from export domain

Require 'delete template' permission on the export domain instead of
'import-export' permission on the template for removing a template from
export domain.

Change-Id: I16755e45c0ac884fd05a6564b201e15a35e34dd5
Bug-Url: https://bugzilla.redhat.com/1010963
Signed-off-by: Arik Hadas <ahadas@redhat.com>