Replace == by === for comparisons in the canvas tests.
Remove wrapFunction from canvas tests.

Its purpose is better served by using step_func_done from plain
testharness.js.
Remove the parallel harness for canvas tests.

These tests predate testharness.js, and have been rewritten to work on top
of it. This commit removes the legacy logging infrastructure.
Remove _assert_throws in favour of assert_throws.
Remove support for annotating crashes in the canvas tests.

This will be handled by the browser automation running the tests.
Mark canvas tests as manual with a yaml property rather than a statement in the code.
Remove duplicated tests.

2d.drawImage.image.incomplete.empty -> 2d.drawImage.incomplete.emptysrc
2d.drawImage.image.incomplete.omitted -> 2d.drawImage.incomplete.removedsrc
2d.gradient.interpolate.zerosize -> 2d.gradient.interpolate.zerosize.fillRect
2d.pattern.image.incomplete.empty -> 2d.pattern.image.incomplete.emptysrc
2d.pattern.image.incomplete.omitted -> 2d.pattern.image.incomplete.removedsrc
Remove outdated canvas tests.

These tests were removed from the submission/ folder in the old HTMLWG
testing repository in changeset 5bfdbef872e3, but were not removed from the
approved/ folder. They were replaced by the 2d.drawImage.incomplete.* and
2d.pattern.image.incomplete.* tests respectively.