Removing the id field from the Action trait

This would in theory be useful for a transposition table, but we do not
currently support that. As such I don't want to burden the
implementation with that field until it is deemed necessary.

src/state.rs

@@ -72,10 +72,7 @@ pub trait GameState: Clone + Debug {
 ///
 /// An action is dependent upon the specific game being defined, and includes
 /// things like moves, attacks, and other decisions.
-pub trait Action: Clone + Debug {
-    /// Returns a uniqie identifier for this action
-    fn id(&self) -> usize;
-}
+pub trait Action: Clone + Debug {}
 
 /// Trait used for players participating in a game
 pub trait Player: Clone + Debug + PartialEq + Eq + Hash {}