chore: removal of database observer

[BenedictHomuth]

Description

This PR removes the last bits of our former observers.

Changelog

• deleted last references and tests from former observers

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• The light- and dark-theme are both supported and tested
• The design was implemented and is responsive for all devices and screen sizes
• The application was tested in the most commonly used browsers (e.g. Chrome, Firefox, Safari)

(Optional) Visual Changes

[github-actions]

The deployment to the dev cluster was successful. You can find the deployment here: https://4235.development.scrumlr.fra.ics.inovex.io
This deployment is only for testing purposes and will be deleted after 1 week.
To redeploy rerun the workflow.
DO NOT STORE IMPORTANT DATA ON THIS DEPLOYMENT

Deployed Images

• ghcr.io/inovex/scrumlr.io/scrumlr-frontend:sha-8b72234

• ghcr.io/inovex/scrumlr.io/scrumlr-server:sha-8b72234

[octomind-dev]

🐙 Octomind

Test Report: 6/14 successful.

description	status	details
About Section Visibility Test	Passed ✅	click
change avatar	Failed ❌	click
check Privacy Policy	Passed ✅	click
check terms & conditions	Passed ✅	click
close cookie banner - front page	Passed ✅	click
close cookie banner - sign-in	Passed ✅	click
create and delete board columns	Failed ❌	click
create_and_delete_notes_and_actions_v2	Failed ❌	click
create lean coffee board	Failed ❌	click
edit_notes_and_actions_v5	Failed ❌	click
get started	Passed ✅	click
share_session	Failed ❌	click
sign-in	Failed ❌	click
test all ways to open the setup flow	Failed ❌	click

commit sha: 8b72234

[mateo-ivc]

lgtm 👍🏽