Remove unnecessary availability check

[rebeccacremona]

Many years ago, we were occasionally finding that, when we uploaded WARCs to S3, they were not immediately available for download, even though the upload was completed. We added a retry to account for this.

Also many years ago, but more recently, Jack looked in to it and reported S3 has since changed, and this inconsistency isn't a problem any more. We decided to keep this check in the codebase anyway, because it was harmless.

Well, now it's causing trouble: we don't have WACZs when new upload-your-own archives are created, because we are still just making WARCs for those. So, the check fails.

Instead of tweaking the check to work properly in both situations, I'm just removing it.

If we find that S3 is, in fact, still inconsistent, then we can add a check back in.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.61%. Comparing base (d4747b8) to head (e631bd3).
Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3655      +/-   ##
===========================================
- Coverage    69.61%   69.61%   -0.01%     
===========================================
  Files           54       54              
  Lines         7350     7339      -11     
===========================================
- Hits          5117     5109       -8     
+ Misses        2233     2230       -3     

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