fixup! fixup! Fix past mis-merges

Author: tautschnig

library/core/src/str/validations.rs

@@ -4,7 +4,6 @@ use super::Utf8Error;
 use crate::intrinsics::const_eval_select;
 #[cfg(kani)]
 use crate::kani;
-use crate::mem;
 
 /// Returns the initial codepoint accumulator for the first byte.
 /// The first byte is special, only want bottom 5 bits for width 2, 4 bits