instance.c: Remove extraneous comments

These comments were added long ago when we didn't have actual
documentation. Now they just add line noise

Change-Id: I00e3ea08220c485841f624c0ccb511455d46b768
Reviewed-on: http://review.couchbase.org/39386
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>