rm plotting from tests

[sneakers-the-rat]

part of the purpose of having automated tests is so that one doesn't need to run a bunch of stuff and manually inspect the output to check if it looks right. plotting should be a separate feature of the package, and the tests should make assertions about the functionality of its components, rather than a means of creating inspectable output.

plotting is also super expensive, so it should probably just be removed, but if it is useful as a debugging step, then it should be moved into some decorator or pytest hook that wraps the tests, and then can be enabled when desired with like pytest --with-plots