Equations for edges and corners.

This is a functional simplification that removes the large arrays in endgames.cpp.
It also fixes a recently introduced bug (960d59d541) in KNBvK,
now using flip_file() instead of ~.

One fen added to bench to increase endgame coverage.

STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 174724 W: 33325 L: 33404 D: 107995
Ptnml(0-2): 2503, 19607, 43181, 19608, 2463
http://tests.stockfishchess.org/tests/view/5e6448ffe42a5c3b3ca2e287

LTC
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 35640 W: 4679 L: 4621 D: 26340
Ptnml(0-2): 189, 2991, 11424, 3005, 211
http://tests.stockfishchess.org/tests/view/5e650b24e42a5c3b3ca2e2d8

closes https://github.com/official-stockfish/Stockfish/pull/2577

Bench: 5527957

src/types.h

@@ -370,10 +370,6 @@ constexpr Piece operator~(Piece pc) {
   return Piece(pc ^ 8); // Swap color of piece B_KNIGHT -> W_KNIGHT
 }
 
-inline File map_to_queenside(File f) {
-  return std::min(f, File(FILE_H - f)); // Map files ABCDEFGH to files ABCDDCBA
-}
-
 constexpr CastlingRights operator&(Color c, CastlingRights cr) {
   return CastlingRights((c == WHITE ? WHITE_CASTLING : BLACK_CASTLING) & cr);
 }