remove nexenta plugin

zfs plugin is better and faster and backward compatible

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>

PVE/Storage/ZFSPlugin.pm

@@ -305,6 +305,10 @@ sub properties {
 	    description => "iscsi provider",
 	    type => 'string',
 	},
+        blocksize => {
+            description => "block size",
+            type => 'string',
+        }
     };
 }