[FormRecognizer] Re-enable live testing with identity-based authentication

[kinelski]

We must migrate samples and tests to use identity-based authentication by default, similar to what's been done to the Document Intelligence package here: #46448

Recently some live tests in this package started hanging indefinitely, preventing our test pipeline from running to finish, and preventing us from re-recording tests after updating them to use identity-based authentication. For this reason, there's not much reason to keep these tests wasting resources, so live testing of the Form Recognizer package has been disabled until the issue is fixed.