@note Due the concurrent nature of the tree, the function extracts <i>nearly</i> maximal key.
It means that the function gets rightmost leaf of the tree and tries to unlink it.
During unlinking, a concurrent thread may insert an item with key great than rightmost item's key.
So, the function returns the item with maximal key at the moment of tree traversing.
@note Due the concurrent nature of the tree, the function extracts <i>nearly</i> maximal key.
It means that the function gets rightmost leaf of the tree and tries to unlink it.
During unlinking, a concurrent thread may insert an item with key great than rightmost item's key.
So, the function returns the item with maximal key at the moment of tree traversing.