This reverts commit 91e9c1c81343990d5ebbb3a3bb7c68ec4445d610.
After feedback, for now we are reverting this change. This is not
permanent, the settings sidebar will be removed again, after we:
* Visually group the settings the same way as the sidebar does
on All Settings
* Add more settings pages to the main admin sidebar to cover the ~250
settings not yet represented there