Revert "use winning_percentage_wdl in learn"

This reverts commit c964e902c5.

# Conflicts:
#	src/uci.cpp

src/uci.cpp

@@ -248,32 +248,6 @@ namespace {
   uint64_t eval_sum;
 } // namespace
 
-
-namespace UCI{
-  // The win rate model returns the probability (per mille) of winning given an eval
-  // and a game-ply. The model fits rather accurately the LTC fishtest statistics.
-  int win_rate_model(Value v, int ply) {
-
-     // The model captures only up to 240 plies, so limit input (and rescale)
-     double m = std::min(240, ply) / 64.0;
-
-     // Coefficients of a 3rd order polynomial fit based on fishtest data
-     // for two parameters needed to transform eval to the argument of a
-     // logistic function.
-     double as[] = {-8.24404295, 64.23892342, -95.73056462, 153.86478679};
-     double bs[] = {-3.37154371, 28.44489198, -56.67657741,  72.05858751};
-     double a = (((as[0] * m + as[1]) * m + as[2]) * m) + as[3];
-     double b = (((bs[0] * m + bs[1]) * m + bs[2]) * m) + bs[3];
-
-     // Transform eval to centipawns with limited range
-     double x = Utility::clamp(double(100 * v) / PawnValueEg, -1000.0, 1000.0);
-
-     // Return win rate in per mille (rounded to nearest)
-     return int(0.5 + 1000 / (1 + std::exp((a - x) / b)));
-  }
-} // namespace UCI
-
-
 // Make is_ready_cmd() callable from outside. (Because I want to call it from the bench command etc.)
 // Note that the phase is not initialized.
 void is_ready(bool skipCorruptCheck)