zfs: fix storagepoolxml2xml test

Commit 7c2d65dd dropped setting default mode.

Update zfs tests accordingly.

tests/storagepoolxml2xmlout/pool-zfs-sourcedev.xml

@@ -10,8 +10,5 @@
   </source>
   <target>
     <path>/dev/zvol/testpool</path>
-    <permissions>
-      <mode>0755</mode>
-    </permissions>
   </target>
 </pool>

tests/storagepoolxml2xmlout/pool-zfs.xml

@@ -9,8 +9,5 @@
   </source>
   <target>
     <path>/dev/zvol/testpool</path>
-    <permissions>
-      <mode>0755</mode>
-    </permissions>
   </target>
 </pool>