oem-config should support debconf option to retain oem user's data

We would like a debconf option to be available to prevent removing the oem user's home directory. Specifically, this amounts to removing the --remove option from the userdel invocation in oem-config-* (when the debconf option is specified).

We are currently using a patched version because we had the issue of people using our fresh distro installation and then eventually running oem-config on accident (or curiousity), causing their existing files to be deleted entirely.

I will admit our use case is not quite what oem-config is designed for, but there are workflows in our organization that prevent proper use, and this tool is still useful despite rather dangerous for us as is (but we patched for now, so it is okay for lucid).