www/py-dj22-django-formset-js-improved: Rename port

• The port was added with the "dj22-" prefix to use Django 2.2 explicitly.
  
  In the meantime most Django ports have been switched from Django 1.11 (End-of-Life) to Django 2.2 (current LTS release).
  
  Hence rename the port to "py-django-formset-js-improved" to be consistent with the names of the other Django ports and to retain the history.

PR: 247032
Approved by: Alexander Sieg (maintainer)