Shortcodes: Module Info updates

The module info included references to `[audio]` and `[upcomingevents]` that shouldn't be there and didn't include the `[gist]` shortcode.

There are a few others that Jetpack has, but there isn't WP.com documentation to point to, so punting those until later.
Are you sure on this? It looks like it is still loading per https://github.com/Automattic/jetpack/blob/4909fe8fe437c9cd2db2a8aefb96fa181aec175d/modules/shortcodes.php#L40