Bug 13746: On creating a new subscription, notes fields get confused

Bug 13746: On creating a new subscription, notes fields get confused

For every subscription we have 4 notes fields in Koha, 2 are in the
subscription itself and another 2 are in the subscription history.

When creating a new subscription, the notes fields from the
subscription get copied to the fields of the subscription history,
leading to doubled up display of notes in the OPAC.

To test:
- Add a new subscription without patch
  - check manual history
  - Fill in both notes fields
- Verify that the notes fields got also saved into the
  subscription history (easy from the Summary tab)
- Apply patch
- Add another subscription, like above
- Verify now only the subscription notes fields are saved
- Edit subscription and notes - verify all is ok
- Edit subscription history (Planning tab) - verify all is ok

Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>