docs: Fix code example (#3135)

Remove Coupon Code doesn't give ErrorResult 
it only return type of Order

docs/docs/guides/storefront/active-order/index.mdx

@@ -190,10 +190,6 @@ To remove a coupon code from the active order, we use the [`removeCouponCode` mu
 mutation RemoveCouponCode($couponCode: String!) {
   removeCouponCode(couponCode: $couponCode) {
     ...ActiveOrder
-    ... on ErrorResult {
-      errorCode
-      message
-    }
   }
 }
 ```