editor: remove showToastNotice apps/web dependency

[hejtful]

The editor is still importing this error handling helper function from serlo.org website.

import { showToastNotice } from '@/helper/show-toast-notice'

For now, it's alright to make the react-hot-toast package a dependency for the editor and duplicate the helper. Afterwards, the editor might get its own redesigned error handling.

[elbotho]

imho one of the nicer handlers we have :) nice dx and only 29 lines of code aside from the react-hot-toast dependency. Would be no problem to duplicate this in the editor if it helps.