chore: remove dash assets section from 'known issues and workarounds' in readme

[dds05]

Description

Chore: Removed [DASH Assets with $Time Interpolation and SegmentTimelines with No t](https://github.com/videojs/http-streaming#dash-assets-with-time-interpolation-and-segmenttimelines-with-no-t) section from 'Known Issues and Workarounds' as it is no longer an issue.

Reference: #256

Specific Changes proposed

Remove the particular section from readme

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

[welcome]

💖 Thanks for opening this pull request! 💖

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[dds05]

• @gkatsev