ZTS: remove verify_slog_support helper

verify_slog_support no longer applies to ZFS since slog support
is always available.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Christian Schwarz <me@cschwarz.com>
Closes #12092

tests/zfs-tests/include/libtest.shlib

@@ -1897,13 +1897,11 @@ function zfs_zones_setup #zone_name zone_root zone_ip
 	block_device_wait
 
 	#
-	# If current system support slog, add slog device for pool
+	# Add slog device for pool
 	#
-	if verify_slog_support ; then
-		typeset sdevs="$TEST_BASE_DIR/sdev1 $TEST_BASE_DIR/sdev2"
-		log_must mkfile $MINVDEVSIZE $sdevs
-		log_must zpool add $pool_name log mirror $sdevs
-	fi
+	typeset sdevs="$TEST_BASE_DIR/sdev1 $TEST_BASE_DIR/sdev2"
+	log_must mkfile $MINVDEVSIZE $sdevs
+	log_must zpool add $pool_name log mirror $sdevs
 
 	# this isn't supported just yet.
 	# Create a filesystem. In order to add this to
@@ -3067,28 +3065,6 @@ function random_get
 	_random_get "$#" "$@"
 }
 
-#
-# Detect if the current system support slog
-#
-function verify_slog_support
-{
-	typeset dir=$TEST_BASE_DIR/disk.$$
-	typeset pool=foo.$$
-	typeset vdev=$dir/a
-	typeset sdev=$dir/b
-
-	mkdir -p $dir
-	mkfile $MINVDEVSIZE $vdev $sdev
-
-	typeset -i ret=0
-	if ! zpool create -n $pool $vdev log $sdev > /dev/null 2>&1; then
-		ret=1
-	fi
-	rm -r $dir
-
-	return $ret
-}
-
 #
 # The function will generate a dataset name with specific length
 # $1, the length of the name