Machine-man and sailor-v previews graduate

Some API previews have graduated and are now an official part of the API. These preview headers are no longer required.

The GitHub App endpoints and endpoints that returned the performed_via_github_app property no longer require the machine-man preview.

application/vnd.github.machine-man-preview+json

For more information, see the "GitHub Apps REST API."

To add and view a lock reason to an issue, you no longer need to use the sailor-v preview.

application/vnd.github.sailor-v-preview+json

For more information about the affected endpoints, see the "Pull Requests" and "Issues" REST APIs.

Thanks again to everyone that tried out these API features during the preview period.