mgmtd, lib: remove batch ids from all messages

mgmtd, lib: remove batch ids from all messages

Batch IDs are only used to verify that all messages were received and
processed by a backend. It's not necessary to do that as we use reliable
stream transport - messages can't be dropped or received out of order.

This commit also fixes possible race condition that can happen if
one backend process messages slower than other backends.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>