tests: get rid of which

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13259

tests/zfs-tests/include/commands.cfg

@@ -109,8 +109,7 @@ export SYSTEM_FILES_COMMON='arp
     uuidgen
     vmstat
     wait
-    wc
-    which'
+    wc'
 
 export SYSTEM_FILES_FREEBSD='chflags
     compress

tests/zfs-tests/include/libtest.shlib

@@ -2618,7 +2618,7 @@ function add_user_linux #<group_name> <user_name> <basedir>
 	# Add new users to the same group and the command line utils.
 	# This allows them to be run out of the original users home
 	# directory as long as it permissioned to be group readable.
-	cmd_group=$(stat --format="%G" $(which zfs))
+	cmd_group=$(stat --format="%G" $(command -v zfs))
 	log_must usermod -a -G $cmd_group $user
 
 	return 0