Do not add unused created attribute to metadata of couch documents on create

[davetsay]

Closes #7655

Describe your changes:

Removed line that adds metadata

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Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
• Has this been smoke tested?
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Reviewer Checklist

• Changes appear to address issue?
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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.10%. Comparing base (f98eb31) to head (6f004da).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7656      +/-   ##
==========================================
- Coverage   49.11%   49.10%   -0.01%     
==========================================
  Files         671      671              
  Lines       27116    27115       -1     
  Branches     2632     2632              
==========================================
- Hits        13318    13315       -3     
- Misses      13470    13472       +2     
  Partials      328      328              

Flag	Coverage Δ
unit	49.10% <ø> (-0.01%)	⬇️

Files	Coverage Δ
...c/plugins/persistence/couch/CouchObjectProvider.js	75.07% <ø> (-1.26%)	⬇️

... and 2 files with indirect coverage changes

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[akhenry]

@davetsay Is this ready for review?