installer still perform the backup for instaltion directory eventhough user uncheck the backup option during the upgrade

Description

When using the installer to perform the backup, it will ask if the admin wants to perform a backup before the upgrade. If the user unchecks the backup option, the installer will still perform the backup.

Steps to reproduce

1. Download a confluence installer
2. Run the installer
3. Select upgrade existing confluence
4. Point to an existing installation directory
5. Uncheck the option to perform backup
6. Click next

Expected result
The upgrade task will proceed without performing the backup

Actual result
The backup is performed before the upgrade.