Revert "Undo unneeded export of CfgRustVersion"

This reverts commit 957824a.

Author: mo8it

crates/cargo-platform/src/lib.rs

@@ -18,7 +18,7 @@ mod cfg;
 mod error;
 
 use cfg::KEYWORDS;
-pub use cfg::{Cfg, CfgExpr, Ident};
+pub use cfg::{Cfg, CfgExpr, CfgRustVersion, Ident};
 pub use error::{ParseError, ParseErrorKind};
 
 /// Platform definition.