net: don't run callbacks on nodes that haven't completed the version handshake

Since ForEach* are can be used to send messages to  all nodes, the caller may
end up sending a message before the version handshake is complete. To limit
this, filter out these nodes. While we're at it, may as well filter out
disconnected nodes as well.

Delete unused methods rather than updating them.

src/net.cpp

@@ -2630,6 +2630,11 @@ void CNode::AskFor(const CInv& inv)
     mapAskFor.insert(std::make_pair(nRequestTime, inv));
 }
 
+bool CConnman::NodeFullyConnected(const CNode* pnode)
+{
+    return pnode && pnode->fSuccessfullyConnected && !pnode->fDisconnect;
+}
+
 void CConnman::PushMessage(CNode* pnode, CSerializedNetMsg&& msg)
 {
     size_t nMessageSize = msg.data.size();
@@ -2680,7 +2685,7 @@ bool CConnman::ForNode(NodeId id, std::function<bool(CNode* pnode)> func)
             break;
         }
     }
-    return found != nullptr && func(found);
+    return found != nullptr && NodeFullyConnected(found) && func(found);
 }
 
 int64_t PoissonNextSend(int64_t nNow, int average_interval_seconds) {