[logging] Don't log REJECT code when transaction is rejected

Remove the BIP61 REJECT code from error messages and logs when a
transaction is rejected.

BIP61 support was removed from Bitcoin Core in
fa25f43ac5. The REJECT codes will be
removed from the codebase entirely in the following commit.

test/functional/feature_bip68_sequence.py

@@ -24,7 +24,7 @@ SEQUENCE_LOCKTIME_GRANULARITY = 9 # this is a bit-shift
 SEQUENCE_LOCKTIME_MASK = 0x0000ffff
 
 # RPC error for non-BIP68 final transactions
-NOT_FINAL_ERROR = "non-BIP68-final (code 64)"
+NOT_FINAL_ERROR = "non-BIP68-final"
 
 class BIP68Test(BitcoinTestFramework):
     def set_test_params(self):