Yes, the book says that a new clearance cancels any previous clearance but I think the book is referring to new clearances in the same "dimension" as the previous one... for example vertically. If you were told "descend FL190 level AVANT" and then told "descend FL150", that would cancel the AVANT restriction unless reiterated.
However, in your case, I think the controller would expect you to comply with the level restriction abeam AVANT.
I cannot see how a direct routing can cancel the level restriction on the descent... by that reasoning... any new clearance would cancel all the previous clearances if not reiterated. Imagine that you were told "turn right 5 degrees" and then "resume own navigation AVANT" ... surely the "turn right" would not cancel the level restriction.