Cleanup benchmark

Avoid unnecessary consecutive ucinewgame commands in benchmark setup.
Remove measuring time and nodes in speedtest warmup.

closes https://github.com/official-stockfish/Stockfish/pull/6427

No functional change

src/benchmark.cpp

@@ -483,7 +483,6 @@ BenchmarkSetup setup_benchmark(std::istream& is) {
     float totalTime = 0;
     for (const auto& game : BenchmarkPositions)
     {
-        setup.commands.emplace_back("ucinewgame");
         int ply = 1;
         for (int i = 0; i < static_cast<int>(game.size()); ++i)
         {