systat: Chase 70ea484e3ec5, removing vdev_cache

[cy]

Summary

As of 70ea484e3ec5 vdev_cache has been removed. Stop reporting on it.
Without this systat reports:

    
sysctl(kstat.zfs.misc.vdev_cache_stats.misses...) failed:
No such file or directory

Test Plan

Tested and working locally.

[mav]

I've never used this zarc sub-command, but looks right. May be the rest should be reviewed too, for example, due to introduction of new "iohit" state between "hit" and "miss".

[cy]

In D40742#926936, @mav wrote:

I've never used this zarc sub-command, but looks right. May be the rest should be reviewed too, for example, due to introduction of new "iohit" state between "hit" and "miss".

Agreed. I think iohit reporting should probably be a separate revision.

[mav]

In D40742#926939, @cy wrote:

Agreed. I think iohit reporting should probably be a separate revision.

Sure. Just bringing to attention.