rpc: remove remains of obsolete log_buffer_size config parameter
    
    The global log buffer feature was deleted in:
    
      commit c0c8c1d7bb53e0420f8573ea961ef7e19b7fff85
      Author: Daniel P. Berrange <berrange@redhat.com>
      Date:   Mon Mar 3 14:54:33 2014 +0000
    
        Remove global log buffer feature entirely
    
        A earlier commit changed the global log buffer so that it only
        records messages that are explicitly requested via the log
        filters setting. This removes the performance burden, and
        improves the signal/noise ratio for messages in the global
        buffer. At the same time though, it is somewhat pointless, since
        all the recorded log messages are already going to be sent to an
        explicit log output like syslog, stderr or the journal. The
        global log buffer is thus just duplicating this data on stderr
        upon crash.
    
        The log_buffer_size config parameter is left in the augeas
        lens to prevent breakage for users on upgrade. It is however
        completely ignored hereafter.
    
        Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
    
    This was in the 1.2.3 release, and 4 years is sufficient time for a
    graceful upgrade path for augeas, so all remaining traces are now
    removed.
    
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>