The Social Form Fill for LinkedIn is not available for new Marketo customers/instances after June 17, 2015. LinkedIn's revised API policy requires Marketo to remove this feature. For all customers and instance prior to the June 17 date, this feature will still be available for a limited time.
For any questions about this policy, please contact LinkedIn Marketing Solutions with questions.
For an alternate solution, customers can use LinkedIn's Autofill. More details on this solution can be found here - LinkedIn Autofill