Remove excess util folder

[andchiind]

Closes #949

Breaking change since some ISAR implementations import the JSON encoder.

Ready for review checklist:

• A self-review has been performed
• All commits run individually
• Temporary changes have been removed, like logging, TODO, etc.
• The PR has been tested locally
• A test has been written
  • This change doesn't need a new test
• Relevant issues are linked
• Remaining work is documented in issues
  • There is no remaining work from this PR that requires new issues
• The changes do not introduce dead code as unused imports, functions etc.

[Christdej]

LGTM