Revert "Added cross-platform default fonts"

Summary:
Revert rPf8ffa393c4427f8b9026075e6dc490990a12df12 (D25021). This Commit caused more grief then fun.

Ref T15630

Test Plan: Site should still be readable on most platforms

Reviewers: O1 Blessed Committers, aklapper

Reviewed By: O1 Blessed Committers, aklapper

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15630

Differential Revision: https://we.phorge.it/D25530