RDKEMW-9835 Systemd service file changes

1. Validating the ai2managers_prereqs.sh script is removed.
2. Validating the sky-appsservice.service, sky-asplayer.service, sky-epg.service and sky-appsservice-vnc.service files are updating with proper ConditionExistsPath
3. Validating the wpeframework-appmanager, downloadmanager, packagemanager, preinstallmanager and lifecyclemanager are removed with ai2managers_prereqs.sh file.