Remove DeepSORT notebook from notebooks repo README.md.

[SkalskiP]

What does this PR do?

Delete the DeepSORT notebook reference from README.md in the notebooks repository. The change reflects the removal of DeepSORT from the Trackers API planned for release 2.1.0.

Type of Change

New feature (non-breaking change that adds functionality)

Testing

• I have tested this change locally
• I have added/updated tests for this change

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in hard-to-understand areas
• My changes generate no new warnings or errors
• I have updated the documentation accordingly (if applicable)