To quote the release notes for AE 2017... 'a 360-degree preset for monoscopic equirectangular video viewing'.
Where is this?
How does it work?
I've gone through all the release note pages, scanned Google.
It got turned into a script snippet instead of a preset, and is included with our scripting updates:
After Effects CC 2017 (14.0) New Scripting Functionality (second script on the page).
Copy it into a text editor and save it as a .jsx file, then run it from File > Run Script...