Remove assert_object_equals.

[sideshowbarker]

See See web-platform-tests/wpt#2030 and https://critic.hoppipolla.co.uk/showcomment?chain=12186

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[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/5727

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[sideshowbarker]

Need to wait for web-platform-tests/wpt#2033 to be resolved before merging this.

[johnmellor]

I've found assert_object_equals useful several times, for example:

• comparing structured clones
• checking that attributes exposed by an binding match an object literal with the expected values

Sometimes you do need to compare two object hierarchies, and it seems unwise to expect people to re-invent the wheel each time.

How about fixing it instead, for example #144