net: remove unnecessary check of CNode::cs_vSend

It is not possible to have a node in `CConnman::vNodesDisconnected` and
its reference count to be incremented - all `CNode::AddRef()` are done
either before the node is added to `CConnman::vNodes` or while holding
`CConnman::cs_vNodes` and the object being in `CConnman::vNodes`.

So, the object being in `CConnman::vNodesDisconnected` and its reference
count being zero means that it is not and will not start to be used by
other threads.

So, the lock of `CNode::cs_vSend` in `CConnman::DisconnectNodes()` will
always succeed and is not necessary.

Indeed all locks of `CNode::cs_vSend` are done either when the reference
count is >0 or under the protection of `CConnman::cs_vNodes` and the
node being in `CConnman::vNodes`.

Author: vasild

src/net.cpp

@@ -1224,19 +1224,10 @@ void CConnman::DisconnectNodes()
         std::list<CNode*> vNodesDisconnectedCopy = vNodesDisconnected;
         for (CNode* pnode : vNodesDisconnectedCopy)
         {
-            // wait until threads are done using it
+            // Destroy the object only after other threads have stopped using it.
             if (pnode->GetRefCount() <= 0) {
-                bool fDelete = false;
-                {
-                    TRY_LOCK(pnode->cs_vSend, lockSend);
-                    if (lockSend) {
-                        fDelete = true;
-                    }
-                }
-                if (fDelete) {
-                    vNodesDisconnected.remove(pnode);
-                    DeleteNode(pnode);
-                }
+                vNodesDisconnected.remove(pnode);
+                DeleteNode(pnode);
             }
         }
     }