qemu: monitor: Remove unused qemuMonitorQueryNamedBlockNodes and clean up

qemu: monitor: Remove unused qemuMonitorQueryNamedBlockNodes and clean up

The top level API is unused so it can be removed but internally the JSON
version is called by other monitor commands which extract information
from the reply.

Thus qemuMonitorJSONQueryNamedBlockNodes is unexported and moved
appropriately.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>