Fix item deletion button which had multiple bugs

[smadbe]

Description

Fix item deletion button which had multiple bugs:

• it was not correctly using the attempt (using the parent or self attempt which does not make sense)
• it was not waiting for the result to be started before fetching the children, which causes an error for instance if you arrive directly on the edition page
• was not handling correctly tasks, was fetching its children

Improvements:

• The remove button has been updated for using change detection OnPush.
• Navigate to the parent instead of going to the root on delete success (much more convenient)

Tests, as the usual user:

• on a chapter with children
• on an empty chapter
• on a task

[smadbe]

[auto-generated message] E2E test report on: https://algorea-static.s3.eu-central-1.amazonaws.com/branch/fix-item-deleting/playwright-report/index.html