The Tempo variable was introduced 10 years ago in our search because the classical evaluation function was antisymmetrical in White and Black by design to gain speed:
Eval(White to play) = -Eval(Black to play)
Nowadays our neural networks know which side is to play in a position when they evaluate a position and are trained on real games, so the neural network encodes the advantage of moving as an output of search. This patch shows that the Tempo variable is not necessary anymore.
Note: there are two locations left in search.cpp where we assume antisymmetry of evaluation (in relation with a speed optimization for null moves in lines 770 and 1439), but as the values are just used for heuristic pruning this approximation should not hurt too much because the order of magnitude is still true most of the time.
