Update unit tests to check unsorted preprocessor output

[chrispcampbell]

When I first added the new unit tests (in read-{subscripts,variables,equations}.spec.ts), the tests that check the output of those phases for the sample tests have the variables in the order produced by the legacy preprocessor at that time, which sorted variables roughly by LHS variable name.

Now that the #575 has been merged (which removed the legacy preprocessor), it's no longer necessary to have those tests compare to the sorted items. It would be more consistent to compare to the definitions in the original order from the source model.

This change only affects the tests, no change in behavior of the compiler.