acme: delete ACME RA account on server uninstall
    
    For each CA server, a Dogtag user account is created for the ACME
    service to use to authenticate to the CA subsystem.  This commit
    cleans up the Dogtag account upon server uninstallation.
    
    The user deletion behaviour is extracted to a common method used for
    both ACME RA account deletion (on uninstall) and removal of the
    temporary admin account (during replica install).
    
    Part of: https://pagure.io/freeipa/issue/4751
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>