Don't emit checksum histograms in ereport.fs.zfs.checksum events

The checksum histograms were intended to be used with ATA and parallel
SCSI, which are obsolete. With modern storage hardware, they will
almost always look like white noise; all bits will be wrong. They only
serve to bloat the event. That's a particular problem on FreeBSD, where
events must fit into a 1016 byte buffer.

This fixes issue #14717 for RAIDZ pools, but not for mirror pools.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Alan Somers <asomers@gmail.com>
Sponsored-by: Axcient
Closes #15052