drop unused metrics domain env var

[dprotaso]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.22%. Comparing base (421c16c) to head (3e733f5).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16019      +/-   ##
==========================================
- Coverage   80.28%   80.22%   -0.06%     
==========================================
  Files         214      214              
  Lines       16904    16904              
==========================================
- Hits        13571    13561      -10     
- Misses       2972     2979       +7     
- Partials      361      364       +3     

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[dsimansk]

/approve
/lgtm

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, dsimansk

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