Possibly this might be the command you want to do the deletion but what i'm unsure of is if there is a command to list the current assigned users.
eeadmin.deassignUser systemNode nodeId dn dnType
Endpoint Encryption user/group de-assignment, allows LDAP users or groups to be de-assigned from an ePO Node or ePO Branch
Change and view user management
systemNode (param 1) - True if nodeId refers to an ePO System, False if nodeId refers to an ePO Branch
nodeId (param 2) - The ID of the ePO System or ePO Branch to de-assign from
dn (param 3) - The LDAP Distinguished Name to be de-assigned.
dnType (param 4) - DN Type, 1 = User, 2 = Group, 3 = OUs (required to avoid an LDAP query)
Not sure if you've already got it but this tool https://community.mcafee.com/docs/DOC-2931 is very handy to view all the possible API commands