need new OSD_SKEWED_USAGE implementation
I've removed the OSD_SKEWED_USAGE implementation because it isn't smart enough:
1. It doesn't understand different CRUSH rules/roots that cover different subsets of devices (e.g., a device class), which means that even a good balance may trigger the warning because different rules have different utilizations (e.g., the ssds are more full than the hdds).
2. It doesn't take into consideration degraded or misplaced objects. Most significantly, when a new, empty disks is added and rebalancing begins you'll get a skewed utilization warning until it is filled up.
The old check is revered in commit d9cfb9c9aea3dbe03962cbaa672b2334903e92c3