Clean up the Backend models

https://gitlab.hzdr.de/hub-terra/sms/backend/-/merge_requests/279#note_1339326

We do have to clean up the Backend models. Three are models and endpoints we don't use anymore like (event, configuration attachments, configuration device, configuration platform)

Please stay with the configuration attachments. We don't them now, but we should add them to the frontend.

However, for those here I agree to remove:

• events
• configuration device
• configureation platform