small tweaks to TestRequestDuplicateBlobHashes

[geoknee]

• Removes some unecessary code which could be confusing
• Adds higher level assertions which are more helpful when there is a bug

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.00%. Comparing base (478b8bd) to head (c5973f6).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #18497      +/-   ##
===========================================
+ Coverage    75.22%   80.00%   +4.77%     
===========================================
  Files          187      132      -55     
  Lines        11199     7168    -4031     
===========================================
- Hits          8425     5735    -2690     
+ Misses        2628     1433    -1195     
+ Partials       146        0     -146     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	80.00% <ø> (+0.37%)	⬆️

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see 57 files with indirect coverage changes

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