Remove associated type `T` on `geo-traits` traits.

[frewsxcv]

• [ ] I agree to follow the project's code of conduct.

• [ ] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

Do we need to specify T for each of the traits?

[kylebarron]

I'm on my phone and can't look at this closely, but I find it very useful to have a compile time generic on the T. I can't quite picture how this would work without the generics.