confmon: Remove 'set_nodes' function (obsolete)

This function is replaced by each individual provider's
configure_nodes() setting.

Change-Id: I22bb7734a7155692f83511b92cd8f7a8947792f1
Reviewed-on: http://review.couchbase.org/37592
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>