The RotateCMSCollectionTypes flag is used in CMS to rotate between the three different kinds of collections of the old generation that CMS has; background collection, foreground collection and full compacting serial GC.
The functionality is only available in non-product builds.
With JDK-8064702 the foreground collector is being removed. This means that there are only two types left. The RotateCMSCollectionTypes flag is not being automatically tested and it is very rarely used. Rather than maintaining it we should remove this functionality. If we need this for debugging in the future it is a pretty simple patch to add back. But for the most part it should be possible to debug in other ways, by for example using ExplicitGCInvokesConcurrent flag and similar.