Remove unused debugging method

src/main/java/org/opentripplanner/street/search/state/State.java

@@ -5,7 +5,6 @@
 import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.List;
 import java.util.Objects;
 import java.util.Set;
 import java.util.stream.Stream;
@@ -482,21 +481,6 @@ public String toString() {
       .toString();
   }
 
-  /**
-   * Iterates over all back states of this instance and returns them as a list.
-   * <p>
-   * Note: Use this only for debugging not for performance-critical paths!
-   */
-  public List<State> chain() {
-    List<State> states = new ArrayList<>();
-    State current = this;
-    while (current != null) {
-      states.add(current);
-      current = current.backState;
-    }
-    return states;
-  }
-
   void checkNegativeWeight() {
     double dw = this.weight - backState.weight;
     if (dw < 0) {