docs: removing duplicated step

[bzenky]

Description

Looking through docs I found a duplicated step

Specific Changes proposed

Remove duplicated step in multiple-alternative-audio-tracks doc

Requirements Checklist

• [ ] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [ ] Unit Tests updated or fixed
  • [ ] Docs/guides updated
  • [ ] Example created (starter template on JSBin)
• [ ] Reviewed by Two Core Contributors

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