[infra-tests] Remove CancellationError (#5733)

Revert https://github.com/w3c/testharness.js/commit/bf0e213dcfb5b3f12e5c3c73b692b7326fc88f47.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5733

Received on Friday, 28 April 2017 13:27:11 UTC