Under Bamboo administration >> Security >> Security settings >> Repository Stored Specs security settings you can enable / disable Specs by clicking on Edit button and defining Enable Repository Stored Specs checkbox.

However, when Repository Stored Specs feature is disabled, Bamboo global administrators are still able to view and edit Linked repository >> [your repository] >> Bamboo Specs tab. Instead, the same should be disabled or hidden indicating the feature is disabled in Security settings.