Jetpack breaks wp_get_shortlink() instead of removing 'wp_shortlink_wp_head' hook!

Jetpack has decided to return an empty string by default when `wp_get_shortlink()` is called for a custom post type. This disables the "shortlink" meta tag and "Get Shortlink" button, but ALSO breaks the WP core `wp_get_shortlink()` function! Jetpack is not the only plugin out there -- `wp_get_shortlink()` is used by other plugins for a variety of reasons -- standard core functionality should not be broken on purpose. Instead of break the `wp_get_shortlink()` function, please use this instead:

```
remove_action( 'wp_head', 'wp_shortlink_wp_head' );
```

Thanks,

js.

Start by tracing Jetpack's handling of wp_get_shortlink() for custom post types and compare it with the issue's suggested wp_shortlink_wp_head action removal. Confirm that wp_get_shortlink() remains usable by other plugins while the shortlink meta tag and Get Shortlink button are disabled; the issue names no file or test to begin with.

Written by the indexing model from the issue text.