Remove "Aleo" as specialized font for headers

Summary: Fixes T11865. Part of a 'clean up remarkup' pass, removing Aleo helps simplify coding, is lighter on the wire, and gives a more consistent, clean look.

Test Plan: run celerity, grep for 'aleo' and 'Aleo', test Phriction, tasks

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11865

Differential Revision: https://secure.phabricator.com/D17535