Improve the deletion of tmp_nodes

[irevoire]

Sometimes we need to delete new nodes previously inserted in the tmp_nodes.
From my understanding, it was always either the last one or the last last one, but it looks like it's not.

It would be good to check measure if we often do a lot of iterations, and if that's the case try to optimize it.

arroy/src/parallel.rs

Line 83 in 5e23882

if let Some(el) = self.ids.iter_mut().rev().take(2).find(|i| **i == item) {