* `make-condition(<condition>)` shouldn't pass `format-string:` and
  `format-arguments:` when creating the condition. Added a new method on
  `<simple-condition>` to do that.

* Consolidate testing of `condition-format-string` and
  `condition-format-arguments` into `test-condition(<simple-condition>)` instead
  of duplicating it for each subclass. These tests don't work for `<type-error>`
  because its format string and args are computed from its type and value slots,
  so add `test-condition(<type-error>)` to prevent calling the next method.

* Remove `do-test-type-error-*` functions. I don't think there's anything much
  to test for `<type-error>`, or most condition classes for that matter, since
  they tend to be plain-old-data classes.

We're choosing one name for the class and it will be <simple-condition>.

Replaces superclass lists like `(<error>, <simple-condition>)` with just
`(<simple-error>)`, and similarly for warnings, where the subclass doesn't need
to be abstract.

Use <simple-condition> instead. There's no point having two names for one class.