chore: remove phone-home telemetry per ASF policy

[skrawcz]

Changes

Remove PostHog usage analytics that collected anonymous data on application builds, execution calls, and CLI commands. ASF projects should not phone home. The burr.telemetry module is kept as a no-op stub (disable_telemetry, is_telemetry_enabled) so existing user code that disables telemetry will not break.

How I tested this

• unit tests

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[github-actions]

A preview of 631802c is uploaded and can be seen here:

✨ https://burr.dagworks.io/pull/669 ✨

Changes may take a few minutes to propagate. Since this is a preview of production, content with draft: true will not be rendered. The source is here: https://github.com/apache/burr/tree/gh-pages/pull/669/