Remove default instances from json

[vzotova]

Type of PR:

• [ ] Bugfix
• [ ] Feature
• [ ] Documentation
• [X] Other

Required reviews:

• [X] 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:

Explain how this PR fits in the greater context of the NuCypher Network. E.g., if this PR addresses a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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