network: allow to handle GetMPTData command if KeepOnlyLatestState enabled

[AnnaShaleva]

Depends on #2095.

We need to adjust server's handleGetMPTDataCmd behaviour wrt KeepOnlyLatestState setting. We also need a test for state exchange between two nodes with KeepOnlyLatestState on.

[roman-khimov]

At the moment KeepOnlyLatestState is ignored when RemoveUntraceable is active which kinda solves the problem (we have all the appropriate data). And and it's a fair behaviour to return whatever MPT data we have (if we don't, this command will error out anyway). So we can remove the check, but there are some other things that can be improved here.