Remove an unnecessary test expectation

[natebosch]

This expect is testing language implementation which is not necessary to
do in this package.

[sigmundch]

This expect is testing language implementation which is not necessary to
do in this package.

Not sure I follow what are you referring to as "a language implementation" here? Maybe the intention here was to test that the source-map parseJson throws when the input is not a simple mapping, but that you need parseJsonExtended to handle that instead?

[sigmundch]

Ah, never mind, back in the day parseJson might have accepted any input and not just Maps.... now that it only accepts Maps I can see how this is unnecessary.