remove all references to InsertOrdered

[gballet]

The InsertOrdered model does not work as well for the verkle conversion, as it doesn't take advantage of the per-level deserialization. This will make the process slower. It also makes things more difficult if the stateful and stateless code are to be merged: that method would have to be supported in a stateless context. Finally, it also contains a lot of duplicated code compared to Insert, which is wasteful.

This PR:

• Removes all references to InsertOrdered;
• In unit tests where it was used to enforce the hashing of nodes, FlushAtDepth is used. Note that the semantics of FlushAtDepth are changed to also hash leaf nodes. This would make things more expensive if we were to use it for the conversion method, but this method is falling out of favor;
• It also improves the ToDot unit test in a stateful context.

[tokenecho]

Is there an alternative? Insert behaves differently than InsertOrdered.