Remove non-functional IAP 2024 option in dropdown

Until #7 is fixed, exclude i24 as it does not have an associated JSON
file. Closes #64.

src/components/Header.tsx

@@ -107,7 +107,7 @@ function getLastUrlName(urlName: string): string {
 }
 
 /** urlNames that don't have a State */
-const EXCLUDED_URLS = ["i23"];
+const EXCLUDED_URLS = ["i23", "i24"];
 
 /** Earliest urlName we have a State for. */
 const EARLIEST_URL = "f22";