Fixes for channel count expvars (#2327)
Fixes for channel count expvars (#2327)

Previously we were double-counting channel readers that were dropped/recreated
tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway,ceejatec/sync_gateway,ceejatec/sync_gateway,couchbaselabs/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway