rustfmt: Drop lightning/src/onion_message/functional_tests.rs from exclusion list

Author: tnull

rustfmt_excluded_files

@@ -53,7 +53,6 @@ lightning/src/offers/payer.rs
 lightning/src/offers/refund.rs
 lightning/src/offers/signer.rs
 lightning/src/offers/test_utils.rs
-lightning/src/onion_message/functional_tests.rs
 lightning/src/onion_message/messenger.rs
 lightning/src/onion_message/mod.rs
 lightning/src/onion_message/offers.rs