chore: drop cloud-cxx-team as CODEOWNERS

[dbolduc]

Drop @googleapis/cloud-cxx-owners (who no longer have Write privileges) as CODEOWNERS.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.68%. Comparing base (5329f71) to head (ded666a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #605   +/-   ##
=======================================
  Coverage   98.68%   98.68%           
=======================================
  Files          50       50           
  Lines        8462     8462           
=======================================
  Hits         8351     8351           
  Misses        111      111           

Flag	Coverage Δ
unittests	98.68% <ø> (ø)

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