ty: erase lifetimes early in `ty::Const::eval`.
ty: erase lifetimes early in `ty::Const::eval`.

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