Remove React Conf announcement bar

[mattcarrollcode]

Related PR: #4560

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[Simek]

Initially, we wanted to replace the promo banner with a link to the React Native Keynote from the conf, when the cut video is available, but I'm also fine with removing it for now. Just wanted to mention it for the context, but leaving that for @cortinico or anyone else from the team to approve.

[cortinico]

Just wanted to mention it for the context, but leaving that for @cortinico or anyone else from the team to approve.

@mattcarrollcode if we do have the Keynote youtube video up, I'd say let's update the banner to point to that video instead for a couple of months

[Simek]

We decided to ship the banner removal for now, and we will follow-up with new banner addition, when cut Keynote video is available. 🙂