tree: tree_destroy_nodes needs to return objects not tree nodes
tree: tree_destroy_nodes needs to return objects not tree nodes

This affects both unbalanced binary search trees as well as red-black trees
since they both use tree_destroy_nodes.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc