Remove -n to set chunk size

This setting is only used by default engine and configured
through passing chunk_size=nn as the configuration value.

Change-Id: I8247920bdfbb560ca10183b33b03ead88e0cb701
Reviewed-on: http://review.couchbase.org/33079
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>