remove format! from assert! (will be an error in rust edition 2021)

src/wallet/mod.rs

@@ -1673,9 +1673,9 @@ mod test {
             let fee_rate = $fee_rate.as_sat_vb();
 
             if !dust_change {
-                assert!((tx_fee_rate - fee_rate).abs() < 0.5, format!("Expected fee rate of {}, the tx has {}", fee_rate, tx_fee_rate));
+                assert!((tx_fee_rate - fee_rate).abs() < 0.5, "Expected fee rate of {}, the tx has {}", fee_rate, tx_fee_rate);
             } else {
-                assert!(tx_fee_rate >= fee_rate, format!("Expected fee rate of at least {}, the tx has {}", fee_rate, tx_fee_rate));
+                assert!(tx_fee_rate >= fee_rate, "Expected fee rate of at least {}, the tx has {}", fee_rate, tx_fee_rate);
             }
         });
     }