You would have to remove them line-by-line. However, you could script this. If you pull the latest config out of the shadow directory, filter out all of the usernames, prepend "no" to those lines, then you can dump them to a parameterized template file for use with Netconfig. Then, you would create a user-defined task in Netconfig which is parameterized, and uses the variable you created in the template file. This way, you could remove all users from every device with one job.
The shadow directory can be found under NMSROOT\files\rme\dmca\shadow on Windows and /var/adm/CSCOpx/files/rme/dcma/shadow on Solaris. More on Netconfig parameterized templates can be found in the RME online help at http://SERVER/help/rme/fundamentals/netcfg_ParametTemplates.html .