Consider removing ReposWithMultipleProjects dashboard

[mikerkelly]

The ReposWithMultipleProjects dashboard was added in #2372, presumably to monitor and reduce the number of such repos. It has not been modified since. There are still 8 such repos. According to this Slack thread (Bennett internal link), we don't and needn't have a policy against such repos. If that's right, we can remove the view which is a minor maintenance win. Probably reversing most of the additions from #2372.

Will ask in #general in Slack if anyone wants the dashboard to remain or is using it for anything.

plausible.io shows 9 visits YTD. According to this Honeycomb trace no users have visited the dashboard in the last sixty days.

[mikerkelly]

We've heard nothing after two days in this Slack thread objecting to removing the dashboard so I think this can go ahead.