refactor(stepfunctions): deprecate unused DISCARD variable and include JsonPath.DISCARD in docs (#26770)

The `DISCARD` variable is removed because it unused. The docs are updated to be more clear to use `JsonPath.DISCARD` for `CatchProps` and `ChoiceProps`.

Closes #26760 .

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: kirkwat

packages/aws-cdk-lib/aws-stepfunctions/lib/states/choice.ts

@@ -19,7 +19,7 @@ export interface ChoiceProps {
   /**
    * JSONPath expression to select part of the state to be the input to this state.
    *
-   * May also be the special value DISCARD, which will cause the effective
+   * May also be the special value JsonPath.DISCARD, which will cause the effective
    * input to be the empty object {}.
    *
    * @default $
@@ -29,7 +29,7 @@ export interface ChoiceProps {
   /**
    * JSONPath expression to select part of the state to be the output to this state.
    *
-   * May also be the special value DISCARD, which will cause the effective
+   * May also be the special value JsonPath.DISCARD, which will cause the effective
    * output to be the empty object {}.
    *
    * @default $

packages/aws-cdk-lib/aws-stepfunctions/lib/states/state.ts

@@ -574,7 +574,7 @@ export function renderList<T>(xs: T[], mapFn: (x: T) => any, sortFn?: (a: T, b:
 }
 
 /**
- * Render JSON path, respecting the special value DISCARD
+ * Render JSON path, respecting the special value JsonPath.DISCARD
  */
 export function renderJsonPath(jsonPath?: string): undefined | null | string {
   if (jsonPath === undefined) { return undefined; }

packages/aws-cdk-lib/aws-stepfunctions/lib/types.ts

@@ -146,7 +146,7 @@ export interface CatchProps {
   /**
    * JSONPath expression to indicate where to inject the error data
    *
-   * May also be the special value DISCARD, which will cause the error
+   * May also be the special value JsonPath.DISCARD, which will cause the error
    * data to be discarded.
    *
    * @default $
@@ -156,5 +156,6 @@ export interface CatchProps {
 
 /**
  * Special string value to discard state input, output or result
+ * @deprecated use JsonPath.DISCARD
  */
-export const DISCARD = 'DISCARD';
+export const DISCARD = 'DISCARD';