Remove instance which is in API now

[smelc]

Note

Requires IntersectMBO/cardano-api#701

This reverts commit c64a1fb.

Changelog

- description: |
    Remove orphan instance that was added to API
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

This instance was temporary (added in #988) and we don't need it anymore, now that it's in API.

[smelc]

Closing: superseded by #1004