Resolve unused variable warnings

[pefoley2]

No description provided.

[gemini-code-assist]

Code Review

This pull request cleans up unused local variables in the Pub/Sub sample files. In iam_samples.cc, the unused topic and subscription variables are removed, and the return values of CreateTopic and CreateSubscription are chained directly to .value(). In topic_admin_samples.cc, an unused google::protobuf::Timestamp timestamp variable is removed. I have no feedback to provide on these changes.

[colinmoy]

/gcbrun

[scotthart]

/gcbrun

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.37%. Comparing base (c0ab3df) to head (484b0ed).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16576      +/-   ##
==========================================
- Coverage   92.38%   92.37%   -0.01%     
==========================================
  Files        2266     2266              
  Lines      219636   219634       -2     
==========================================
- Hits       202903   202896       -7     
- Misses      16733    16738       +5     

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