Make workItemCount() smarter for htmlCacheUpdate/refreshLinks
Do not count jobs that just make subdivide as having any
"work items". This makes $wgJobBackoffThrottling less
overzealous when used to limit these type of jobs.
The main reason to limit htmlCacheUpdate would be for
CDN purge rate limiting. For refreshLinks, it would
mostly be lag, though that is already handled for
leaf jobs and JobRunner itself.