Delete ManagedChannelUtil, which is only used in tests

[jack-berg]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.30%. Comparing base (47c970d) to head (8115baf).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8244      +/-   ##
============================================
- Coverage     90.31%   90.30%   -0.01%     
+ Complexity     7652     7651       -1     
============================================
  Files           843      842       -1     
  Lines         23087    23075      -12     
  Branches       2312     2312              
============================================
- Hits          20851    20839      -12     
  Misses         1517     1517              
  Partials        719      719              

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