This was never used, so let's get rid of it.

The two are equivalent, but really we want to check the HTTP result that got
returned to the channel, not the code that the Request object *intended* to
return to the channel.

The root resource isn't necessarily a JsonResource, so rename this method
accordingly, and update a couple of test classes to use the method rather than
directly manipulating self.resource.

This converts calls like super(Foo, self) -> super().

Generated with:

    sed -i "" -Ee 's/super\([^\(]+\)/super()/g' **/*.py

Sometimes it's useful for synapse to generate its own .well-known file.