azure-update: Clean up ADU group, device class, device & deployment

Azure Device Update has a per-instance limit of 100 device groups and 80
device classes. Once the limit is reached, no more groups or device
classes can be created and this results in deployment failures in CI
runs.

Add deletion of group and device class to the cleanup command. Because
Azure only allows deleting empty groups which have no devices or
deployments, we also query and delete the group's associated device and
deployment.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>