Remove 'future Rust version' code block in diagnostic text.
Remove 'future Rust version' code block in diagnostic text.

Fixes https://github.com/rust-lang/rust/issues/43780.

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