LPS-38694 Subscriptions to content on Private Pages persist after leaving the Site in the My Subscriptions Portlet

Hey Hugo,

I'm sending you two different fixes for this issue to hopefully speed up this process due to the time zone difference.

In regards to your questions:

1. In both these pulls I moved the clean up logic to UserServiceImpl

2. It is not removing all of the subscriptions, just the ones that the user no longer has permission to view.

3. This is why I have two pull requests: This one does it based on permissions and the other one does it based on the group being left. The issue with removing subscriptions based on the group is that there is no groupId included in the subscription table, so it took some coding to grab the groupId.

I'll link the second commit in the comments. Let me know what you think.