Rename stake-address-info field: stakeDelegation -> delegation for eras prior to Conway

[carbolymer]

Changelog

- description: |
    Rename stake-address-info field: stakeDelegation -> delegation for eras prior to Conway
# 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
  # - improvement    # QoL changes e.g. refactoring
   - 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...

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[carlhammann]

Even if we'll (I'll) probably have to rework this a bit more (see #417 and #353), it's good to keep track of this requirement by adding it to the code that's already commited.