Simplify pawn asymmetry (remove use of semiopen files). (#2054)

This is a functional simplification.

To me, the exclusive OR of semiopenFiles here is quite convoluted. Looks like it can be removed.

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 43885 W: 9731 L: 9653 D: 24501
http://tests.stockfishchess.org/tests/view/5c9041680ebc5925cfff10ea

LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 68437 W: 11577 L: 11533 D: 45327
http://tests.stockfishchess.org/tests/view/5c9101740ebc5925cfff1cbf

bench 3575627

src/evaluate.cpp

@@ -743,12 +743,12 @@ namespace {
                             && (pos.pieces(PAWN) & KingSide);
 
     // Compute the initiative bonus for the attacking side
-    int complexity =   9 * pe->pawn_asymmetry()
+    int complexity =   9 * pe->passed_count()
                     + 11 * pos.count<PAWN>()
                     +  9 * outflanking
                     + 18 * pawnsOnBothFlanks
                     + 49 * !pos.non_pawn_material()
-                    -121 ;
+                    -103 ;
 
     // Now apply the bonus: note that we find the attacking side by extracting
     // the sign of the endgame value, and that we carefully cap the bonus so
@@ -776,7 +776,7 @@ namespace {
         if (   pos.opposite_bishops()
             && pos.non_pawn_material(WHITE) == BishopValueMg
             && pos.non_pawn_material(BLACK) == BishopValueMg)
-            sf = 8 + 4 * pe->pawn_asymmetry();
+            sf = 16 + 4 * pe->passed_count();
         else
             sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);