maxColdDBCount never did anything from 4.0 on. It does not and never did (even under version 3.x) delete or remove buckets from the cold store. It was used purely for search and memory resource management internally in 3.x, and had no effect in 4.x and up.
To manage space used on the cold store, in 4.2.x, you can (and should) use the volume limit settings. In 4.1 and 4.0, you would use maxTotalDataSizeMB, at least indirectly.
