Deleting a project link stops the two projects from sharing information.
If you have set up multiple project links to the same application, for example you have linked a Confluence space to multiple JIRA projects, deleting the primary link will mean that another of the links will be made the primary link.
To delete a project link:
Click 'Application Links' in the left-hand panel.
Click the 'Delete' link next to the link that you want to delete.
A confirmation screen will appear. Click the 'Confirm' button to delete the link.
Screenshot above: Confirming the deletion of a project link