Use strip_{prefix|suffix} instead of {starts|ends}_with+indexing

compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

@@ -390,13 +390,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     if let Some((name, term)) = associated_ty {
                         // FIXME: this case overlaps with code in TyCtxt::note_and_explain_type_err.
                         // That should be extracted into a helper function.
-                        if constraint.ends_with('>') {
-                            constraint = format!(
-                                "{}, {} = {}>",
-                                &constraint[..constraint.len() - 1],
-                                name,
-                                term
-                            );
+                        if let Some(stripped) = constraint.strip_suffix('>') {
+                            constraint = format!("{stripped}, {name} = {term}>");
                         } else {
                             constraint.push_str(&format!("<{name} = {term}>"));
                         }