fix usage bug of fluid.data (#4629)

* take fluid.layers.data in place of fluid.data
* delete create_var_list_v2 func
* fix usage bug of fluid.data

PaddleCV/tracking/pytracking/libs/Fconv2d.py

@@ -72,10 +72,10 @@ def Fconv2d(
                     groups mismatch.
     Examples:
         .. code-block:: python
-          data = fluid.data(name='data', shape=[3, 32, 32], \
+          data = fluid.data(name='data', shape=[None, 3, 32, 32], \
                                   dtype='float32')
           filter = fluid.data(name='filter',shape=[10,3,3,3], \
-                                    dtype='float32',append_batch_size=False)
+                                    dtype='float32')
           conv2d = fluid.layers.conv2d(input=data,
                                        filter=filter,
                                        act="relu")