Fix string check in uninstall helper
The install helpers used an invalid string check. ``('ubuntu')`` is
not a tuple. It's a string with superfluous parenthesis. A single-item
tuple would be ``('ubuntu',)``. It's recommended to use set literals to
avoid such mistakes.
Also check for 'debian' platform.
Fixes: https://pagure.io/freeipa/issue/8937
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>