No longer testing against rust panic messages

[UnsignedByte]

An issue I noticed recently when updating the rust version is that our error messages changed due to the update of rust. #429 shows some of the changes in the .expect files. I mentioned this to adrian and he recommended maybe stepping away from relying on rust's error messages and using our own error system more, and I agree.

I think we have a weird combination at the moment of some compiler errors having our nice error system and some others just being thread 'main panicked..., and at some point we should clean this up to make it more readable and in the case that we ever make a release build which might not have all this debug info.

Pretty low priority but something to keep on the radar.