rustfmt: Drop util/indexed_map.rs from exclusion list

Author: tnull

rustfmt_excluded_files

@@ -72,7 +72,6 @@ lightning/src/routing/router.rs
 lightning/src/routing/scoring.rs
 lightning/src/routing/test_utils.rs
 lightning/src/routing/utxo.rs
-lightning/src/util/indexed_map.rs
 lightning/src/util/invoice.rs
 lightning/src/util/logger.rs
 lightning/src/util/macro_logger.rs