A king move can never have negative SEE

So there is no need to explicitly check for king moves
when detecting prunable evasions.

Perhaps teoretically a very bit slower (I didn't test),
but it is more clear now what evasions we consider prunable.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/search.cpp

@@ -1502,7 +1502,6 @@ namespace {
       evasionPrunable =   isCheck
                        && bestValue > value_mated_in(PLY_MAX)
                        && !pos.move_is_capture(move)
-                       && pos.type_of_piece_on(move_from(move)) != KING
                        && !pos.can_castle(pos.side_to_move());
 
       // Don't search moves with negative SEE values