refactor: remove unnecessary judgment when check fragment props

[gebilaoxiong]

There is a small problem with the judgment here.

When we define key in props we use the descriptor like this

  Object.defineProperty(props, 'key', {
    get: warnAboutAccessingKey,
    configurable: true,
  });

When enumerable is not defined, the default value is false.
doc: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

So when we use Object.keys to get the fragement props, we will never get the key.
code: https://github.com/facebook/react/blob/master/packages/react/src/ReactElementValidator.js#L239

[pull-bot]

Details of bundled changes.

Comparing: 9a110eb...91a971b

schedule

File	Filesize Diff	Gzip Diff	Prev Size	Current Size	Prev Gzip	Current Gzip	ENV
schedule.development.js	n/a	n/a	0 B	19.17 KB	0 B	5.74 KB	UMD_DEV
schedule.production.min.js	n/a	n/a	0 B	3.16 KB	0 B	1.53 KB	UMD_PROD

Generated by 🚫 dangerJS

[gaearon]

What's the point of specifying the default value explicitly?

[gebilaoxiong]

@gaearon

If we continue to use Object.keys later
We can intuitively find there is no need to judge key and ref..

If it is not necessary, I can remove it.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution.