random: drop ad-hoc Shuffle in favor of std::shuffle

Benchmarks show it is no longer faster with modern standard C++ libraries,
and the debug-mode failure due to self-move has been fixed as well.

src/net.h

@@ -1625,7 +1625,7 @@ private:
                 }
             }
             if (shuffle) {
-                Shuffle(m_nodes_copy.begin(), m_nodes_copy.end(), FastRandomContext{});
+                std::shuffle(m_nodes_copy.begin(), m_nodes_copy.end(), FastRandomContext{});
             }
         }