This is just a more detailed annotation than was previously provided by the mysterious Amount credited label. The line and number were always there.
If you really want to get rid of it, that will require a custom theme with a bunch of conditional logic in the section that loops through the table.totals array. But that’s beyond the scope of this forum.
Remember that these do not appear when you send a new invoice to a customer, unless there has been a credit waiting to be applied in that customer’s account. In that case, I’m sure the customer would be happy to see it. The point of the increased information is to make it more obvious which payments or credits have been applied after the fact. That can also be useful if you get a partial payment and need to resend the invoice as a reminder.