[CONFIGURATION] File configuration - remove zipkin

[marcalff]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

• Follow up on Delete ZipkinSpanExporter opentelemetry-configuration#453
• Remove support for "zipkin" in file configuration, since it was removed from the model schema.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.93%. Comparing base (025a3b9) to head (ed681f4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3804   +/-   ##
=======================================
  Coverage   89.93%   89.93%           
=======================================
  Files         225      225           
  Lines        7163     7163           
=======================================
  Hits         6441     6441           
  Misses        722      722           

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