temporarily switch to tf.tensordot instead of tensordot2 (#941)

* remove tensordot2; it has a bug

* remove another tensordot2 call

Author: mganahl

tensornetwork/backends/tensorflow/tensorflow_backend.py

@@ -16,7 +16,6 @@
 from typing import Union
 from tensornetwork.backends import abstract_backend
 from tensornetwork.backends.tensorflow import decompositions
-from tensornetwork.backends.tensorflow import tensordot2
 import functools as fct
 import operator as op
 
@@ -46,7 +45,7 @@ def __init__(self) -> None:
 
   def tensordot(self, a: Tensor, b: Tensor,
                 axes: Union[int, Sequence[Sequence[int]]]) -> Tensor:
-    return tensordot2.tensordot(tf, a, b, axes)
+    return tf.tensordot(a, b, axes)
 
   def reshape(self, tensor: Tensor, shape: Tensor) -> Tensor:
     return tf.reshape(tensor, shape)
@@ -108,7 +107,7 @@ def convert_to_tensor(self, tensor: Tensor) -> Tensor:
     return result
 
   def outer_product(self, tensor1: Tensor, tensor2: Tensor) -> Tensor:
-    return tensordot2.tensordot(tf, tensor1, tensor2, 0)
+    return tf.tensordot(tensor1, tensor2, 0)
 
   #pylint: disable=unused-argument
   def einsum(self,