chore(internal/legacylibrarian): remove google-cloud-go generate from automation

[JoeWang1127]

Remove google-cloud-go from generate automation, prepare for librarian Go migration.

[gemini-code-assist]

Code Review

This pull request updates the legacy automation configuration by removing the 'generate' command from the supported commands for the 'google-cloud-go' repository. I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.38%. Comparing base (183bb51) to head (8da02e0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4853   +/-   ##
=======================================
  Coverage   81.38%   81.38%           
=======================================
  Files         130      130           
  Lines       10910    10910           
=======================================
  Hits         8879     8879           
  Misses       1392     1392           
  Partials      639      639           

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