TC-39 recently decided to remove the Python-based testing harness from the
Test262 project [1]. The code has been duplicated in a standalone project;
update V8's dependencies to fetch from that new location. This is based on
an earlier patch by Mike Pennisi.

[1] https://github.com/tc39/tc39-notes/blob/2b9722db9b90011d6083a5f1c8ff1559cbe01c0b/es7/2016-05/may-25.md

BUG=v8:5078

Review-Url: https://codereview.chromium.org/2131743002
Cr-Commit-Position: refs/heads/master@{#37985}