Do not specify type in generated let bindings.
Do not specify type in generated let bindings.

This avoids issues with `impl_trait_in_bindings` as the type from the
argument is normally used as the let binding, but `impl Trait` is
unstable in binding position.

aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust