[position] Remove castle module (it went to board)

position/src/position.rs

@@ -1,11 +1,9 @@
 // Eryn Wells <eryn@erynwells.me>
 
-mod castle;
 mod make_move;
 mod position;
 
 pub use {
-    castle::CastleEvaluationError,
     make_move::{MakeMoveError, ValidateMove},
     position::Position,
 };