Delete another problematic XML test file

Summary: Ref T7215. This test is occasionally failing for me locally. Remove it as per D13992.

Test Plan: arc unit

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T7215

Differential Revision: https://secure.phabricator.com/D14027