Remove sim codegen from near_bindgen

[austinabell]

This cannot happen now since we need a smooth transition from sim tests, but can be purged in the next major release/pre-release

This involves just removing the `

{Struct Name}

Contractproxy structures used by sim. If we continue with this pattern, which is a bit redundant if the functionality is linked with ACI and requires the use ofrlib` on the crate, it will likely be completely re-written anyway