rustfmt: Drop util/mod.rs from exclusion list

Author: tnull

rustfmt_excluded_files

@@ -73,5 +73,4 @@ lightning/src/routing/test_utils.rs
 lightning/src/routing/utxo.rs
 lightning/src/util/invoice.rs
 lightning/src/util/message_signing.rs
-lightning/src/util/mod.rs
 lightning/src/util/string.rs