Remove ambiguity about info.version

In [OpenAPI.next versions/3.0.md](https://github.com/OAI/OpenAPI-Specification/blob/OpenAPI.next/versions/3.0.md#infoObject) `info.version` is marked **Requried**, then the second sentence starts "While not required, ". Some may be confused and think this starts a contradiction. I suggest not adding this sentence at all, as it only raises additional questions (is "application API === "API definition"?) I propose more concise rephrasing.