The "migrate" field should not be displayed on directive creation
When we create a directive based on a technique for which several version are available, we must hide the part of the form with "migrate" and only display the current technique version.
If the user tries to change version during creation ("oups, I wanted to use the previous technique version"), whatever he does will fail:
- changing the version and hitting "save" will just not change the version,
- changing the version and hitting "migrate" leads to a blank edition zone (certainly an error when the form tries to find information from a not yet existing directive).