feature: Remove exgentic

[esnible]

Feature Description

https://github.com/rossoctl/examples/tree/main/a2a/exgentic_agent does not have usable instructions.

Proposed Solution

Remove code and leave a README pointing to https://github.com/rossoctl/workload-harness/

Want to contribute?

• I would like to work on this issue.

Additional Context

No response

[github-actions]

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