[web] Remove fontsource

Summary:
See context in ENG-848 – on prod it's not working, and it's causing serious performance effects on the Node server backend as well as causing the website to take 15s to load.

As of D3122 (which "fixed" ENG-675), the fonts are getting loaded from Google Fonts anyways. These lines aren't working, so there should be no negative impact to removing them.

Test Plan: Best I can do is test yarn prod in my local environment. From investigating the prod web environment with Chrome Dev Tools, I'm pretty sure this is a safe change

Reviewers: atul, benschac, palys-swm

Reviewed By: atul

Subscribers: Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3372