The functions ringbuf_read_completion() and monitor_get_rs()
are not used anywhere anymore, so let's remove them.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>