Revert "Make it possible to run VisualEditor tests in headless mode"

This reverts commit 9a20fc03b75fffc83dffc3e17190279f526e0072.

This change appears to have completely broken the VisualEditor browser tests :(

Change-Id: Ia2753f0718ccc5ac5ce7b726bd89040171feae7c
Merge "Revert "Make it possible to run VisualEditor tests in headless mode""