Use new datamodelling converter by default in backend

[RonnyB71]

Description

Currently the old XSD => Json Schema converter code is used when uploading an XSD from the new datamodelling tool. It's connected to the decision on keeping Seres (now reverted) which introduced a concept of XSD centric (ie. use old converter) and Json Schema centric (ie. use new converter) in the code base. These concepts needs to be removed and the new datamodelling tool should use the new converter.

The new tool uses the DatamodelsController, the old uses ModelController. Only code in DatamodelsController should be changed.

Tasks

• [x] Remove the code that switches between the new and old converter¨
• [x] Remove the concepts of XSD Centric and Json Schema centric from the code
• [ ] Clean up DatamodelsController and remove endpoints no longer in use.

Acceptance Criterias

• [x] XSD's that are uploaded through the new tool should use the new backend code to convert from XSD to Json Schema
• [x] XSD centric and Json Schema centric consepts are removed from the code bases
• [ ] DatamodelsController only exposes endpoints used by new datamodelling tool