zpool-remove.8: describe top-level vdev sector size limitation

Document that top-level vdevs cannot be removed unless all top-level
vdevs have the same sector size.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Sam Hathaway <sam@sam-hathaway.com>
Closes openzfs#11339
Closes openzfs#12472

man/man8/zpool-remove.8

@@ -52,10 +52,10 @@
 Removes the specified device from the pool.
 This command supports removing hot spare, cache, log, and both mirrored and
 non-redundant primary top-level vdevs, including dedup and special vdevs.
-When the primary pool storage includes a top-level raidz vdev only hot spare,
-cache, and log devices can be removed.
-Note that keys for all encrypted datasets must be loaded for top-level vdevs
-to be removed.
+.Pp
+Top-level vdevs can only be removed if the primary pool storage does not contain
+a top-level raidz vdev, all top-level vdevs have the same sector size, and the
+keys for all encrypted datasets are loaded.
 .Pp
 Removing a top-level vdev reduces the total amount of space in the storage pool.
 The specified device will be evacuated by copying all allocated space from it to