Remove Wal-Mart, is broken

This API is broken.

Return: HTTP Code 404

Ref: #1590
Ref: https://github.com/public-apis/public-apis/runs/3368073631?check_suite_focus=true#step:3:24

README.md

@@ -943,7 +943,6 @@ API | Description | Auth | HTTPS | CORS |
 | [Dummy Products](https://dummyproducts-api.herokuapp.com/) | An api to fetch dummy e-commerce products JSON data with placeholder images | `apiKey` | Yes | Yes |
 | [eBay](https://go.developer.ebay.com/) | Sell and Buy on eBay | `OAuth` | Yes | Unknown |
 | [Etsy](https://www.etsy.com/developers/documentation/getting_started/api_basics) | Manage shop and interact with listings | `OAuth` | Yes | Unknown |
-| [Wal-Mart](https://developer.walmartlabs.com/docs) | Item price and availability | `apiKey` | Yes | Unknown |
 | [Wegmans](https://dev.wegmans.io) | Wegmans Food Markets | `apiKey` | Yes | Unknown |
 
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