remove duplicate additionalPrinterColumns

[k4leung4]

patch for knative/serving#14592

remove duplicate 'additionalPrinterColumns' in domain-mapping resource, was seeing

error: map[string]interface {}(nil): yaml: unmarshal errors:
  line 153: mapping key "additionalPrinterColumns" already defined at line 31

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (97f6b43) 70.76% compared to head (813de05) 70.76%.
Report is 2 commits behind head on main.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #192   +/-   ##
=======================================
  Coverage   70.76%   70.76%           
=======================================
  Files           4        4           
  Lines         195      195           
=======================================
  Hits          138      138           
  Misses         40       40           
  Partials       17       17           

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