There is no built-in way to do this, I'm afraid. A developer may be able to do something clever to hide it using javascript after the form as been submitted, possibly.
@LiveLu / @Phil_Vallender - instead of using the form title ---- I would just copy the HTML and use a Paragraph (Rich Text) field as the top field on the form itself. That way, if your using an inline message only THAT inline message text will show AFTER the form submission.
There is no built-in way to do this, I'm afraid. A developer may be able to do something clever to hide it using javascript after the form as been submitted, possibly.