Remove empty categories from categories.yml
Remove empty categories from categories.yml

These categories have not been used since
9369fce8839de5eedd772c27f993ea513cd7934a, but they currently remain in
the sidebar. This removes them completely.

airbrake/airbrake-docs,airbrake/airbrake-docs,airbrake/airbrake-docs,airbrake/airbrake-docs