Allow removing policy project

What does this MR do?

We can assign policy project to project but form submit won't work if we want to unassign policy project from project. This MR extends the service to achieve that.

Mr also addresses some FE issues

Screenshots

After removing

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have not included a changelog entry because of its behind feature flag.
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