[TASK] Use flash message in CreatePageWizard

Instead of using some old code, a flash message is better.

furthermore a not used function is removed

Resolves: #49637
ReleaseS: 6.2
Change-Id: I6f444da59df77d81d8948b3940e17703f1cecdc2
Reviewed-on: https://review.typo3.org/21843
Reviewed-by: Mattias Nilsson
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer