fix(apidom-ns-openapi-3-0): semantic highlighting for responses

[robert-hebel-sb]

Fix highlighting default responses by removing default key from fixed parameters

How Has This Been Tested?

unit test + tested manually on local env

Screenshots (if appropriate):

Checklist

My PR contains...

• [ ] No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• [ ] Dependency changes (any modification to dependencies in package.json)
• [ ] Bug fixes (non-breaking change which fixes an issue)
• [ ] Improvements (misc. changes to existing features)
• [ ] Features (non-breaking change which adds functionality)

My changes...

• [ ] are breaking changes to a public API (config options, System API, major UI change, etc).
• [ ] are breaking changes to a private API (Redux, component props, utility functions, etc.).
• [ ] are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• [ ] are not breaking changes.

Documentation

• [ ] My changes do not require a change to the project documentation.
• [ ] My changes require a change to the project documentation.
• [ ] If yes to above: I have updated the documentation accordingly.

Automated tests

• [ ] My changes can not or do not need to be tested.
• [ ] My changes can and should be tested by unit and/or integration tests.
• [ ] If yes to above: I have added tests to cover my changes.
• [ ] If yes to above: I have taken care to cover edge cases in my tests.
• [ ] All new and existing tests passed.