Remove cfg(test) from library/core

Author: saethlin

Diff for: core/src/error.rs

@@ -1,9 +1,6 @@
 #![doc = include_str!("error.md")]
 #![stable(feature = "error_in_core", since = "1.81.0")]
 
-#[cfg(test)]
-mod tests;
-
 use crate::any::TypeId;
 use crate::fmt::{Debug, Display, Formatter, Result};
 

Diff for: core/tests/lib.rs

@@ -141,7 +141,6 @@ mod intrinsics;
 mod io;
 mod iter;
 mod lazy;
-#[cfg(test)]
 mod macros;
 mod manually_drop;
 mod mem;