Serve sites map directly from https://api.nasqueron.org

Summary:
Don't proxy anymore sites.json, as D1303 introduced CORS support.

This is a follow-up for cd026d254f2fe.

Test Plan:
Browse main page, use "g t" to go to Nasqueron Tools,
ensure there isn't any CORS-related error in console.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1304