Project import tries to import groups for any project's comment visibility field

When doing project import, jira will require in the destination instance all groups that have been used as 'Viewable By' in any comment for all projects in the original backup.

Steps to reproduce:

1. Have a Jira instance with two projects, A and B
2. In the Admin > General Configuration, set "Groups & Project Roles" in the Comment visibility
3. In project A, add a comment viewable by a specific group that does not exist in the destination instance.
4. take a backup of the Jira instance
5. In the destination instance, try to import project B

The project importer will require the existence of the group, even though the comment is in a different project. Jira should only require the groups that have been used in the viewable by in the comments for the project we are trying to import.