xfstests: generic/273: use src/feature -o

Due to partially committed series (fd080d64b6)
generic/273 test uses '_no_of_online_cpus' function which is not defined.

Now it's safe to switch it to 'src/feature -o'.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>

tests/generic/273

@@ -47,7 +47,7 @@ count=2
 
 _threads_set()
 {
-	_cpu_num=`_no_of_online_cpus`
+	_cpu_num=`$here/src/feature -o`
 	threads=$(($_cpu_num * 50))
 	if [ $threads -gt 200 ]
 	then