(maint) Improve tests for slurp on define/class

The tests for define and class rejecting `*` parameters put another
parameter after the one specified with `*`. This created an ambiguity in
the test for why it is failing, since `*` is not allowed before any
other parameters. Since the assertion is that define and class simply
cannot have `*` parameters, the better test is to have a single
parameter with a `*`.