Summary: Fixes T12013. Send either "Content-Length" or enable output compression, but not both. Prefer compression for static resources (CSS, JS, etc). Test Plan: Ran `curl -v ...`, no longer saw responses with both compression and `Content-Length`. Reviewers: chad, avivey Reviewed By: avivey Subscribers: avivey Maniphest Tasks: T12013 Differential Revision: https://secure.phabricator.com/D17045