How to migrate a Jira project from Jira Enterprise (with crowd) to Jira Professional

We are running Atlassian JIRA Enterprise 3.13.2 with Atlassian Crowd as SSO system and use it for our client projects. Once and a while we have to move the JIRA project from our jira enterprise installation to a jira instance at the client side for later reference. This is exactly what I had to do a couple of days ago.