wallet: kill support for deprecated ephemeral Boost messages

The commit kills support for deprecated ephemeral Boost messages: signed/unsigned transaction sets, pending transactions, reserve proofs, MMS messages, etc.
It does NOT kill support for loading very old wallets in Boost format, that should be supported indefinitely. These messages were deprecated 5 years ago. Since
then, we have had a hard fork to enable a new non-compatible transaction type (w/ view tags), and disable the old transaction type. This renders basically all
of the aforementioned messages before that HF useless, with the possible exception of reserve proofs.

This commit also cleans up dead inclusions of boost serialization headers.

This commit is part of upstreaming Carrot/FCMP++. Killing support for Boost messages now means less boilerplate Boost serialization review for Carrot/FCMP++.

src/wallet/wallet_rpc_server.cpp

@@ -1890,18 +1890,6 @@ namespace tools
     }
     catch(...) {}
 
-    if (!loaded && !m_restricted)
-    {
-      try
-      {
-        std::istringstream iss(blob);
-        boost::archive::portable_binary_iarchive ar(iss);
-        ar >> ptx;
-        loaded = true;
-      }
-      catch (...) {}
-    }
-
     if (!loaded)
     {
       er.code = WALLET_RPC_ERROR_CODE_BAD_TX_METADATA;