Remove default instances from json

[vzotova]

Type of PR:

• Bugfix
• Feature
• Documentation
• Other

Required reviews:

• 1
• 2
• 3

What this does:

High-level idea of the changes introduced in this PR.
List relevant API changes (if any), as well as related PRs and issues.

Issues fixed/closed:

• Fixes #...

Why it's needed:

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E.g., if this PR addresses a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

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[derekpierre]

🎸

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.55%. Comparing base (d540b7c) to head (ff4dd3e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   90.55%   90.55%           
=======================================
  Files          18       18           
  Lines         900      900           
=======================================
  Hits          815      815           
  Misses         85       85           

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