Remove bgfetcher retry code

Change-Id: Ic87e1506a5ec5b8f7786c73064101871a63ddf36
Reviewed-on: http://review.couchbase.org/40959
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>