chore(template-require-mandatory-role-attributes): drop dead createRequiredAttributeErrorMessage

The helper was unused after the messageId migration (the rule now uses
aria-query-derived data + `messages.missingRequired` with a parameterized
template). No references remained in the rule or its test file.

Author: johanrd

lib/rules/template-require-mandatory-role-attributes.js

@@ -1,13 +1,5 @@
 const { roles } = require('aria-query');
 
-function createRequiredAttributeErrorMessage(attrs, role) {
-  if (attrs.length < 2) {
-    return `The attribute ${attrs[0]} is required by the role ${role}`;
-  }
-
-  return `The attributes ${attrs.join(', ')} are required by the role ${role}`;
-}
-
 // ARIA role values are whitespace-separated tokens compared ASCII-case-insensitively.
 // Returns the list of normalised tokens, or undefined when the attribute is
 // missing or dynamic.