fix(variables): simplify answer node variable extraction

Replace complex variable mapping with direct answer field access for Answer nodes to improve efficiency and maintainability.

web/app/components/workflow/nodes/_base/components/variable/utils.ts

@@ -948,9 +948,7 @@ export const getNodeUsedVars = (node: Node): ValueSelector[] => {
       break
     }
     case BlockEnum.Answer: {
-      res = (data as AnswerNodeType).variables?.map((v) => {
-        return v.value_selector
-      })
+      res = matchNotSystemVars([(data as AnswerNodeType).answer])
       break
     }
     case BlockEnum.LLM: {