message: Don't assign Tensor._shape in control_flow_ops.py
  I'm not totally sure why this was done to begin with. However, nothing
  seems to break with it removed. I'd like to remove this since setting
  _shape won't work with the C API enabled.
diff: @@ -2468,7 +2468,6 @@ class WhileContext(ControlFlowContext):
  zeros_shape = array_ops.shape_internal(value, optimize=False)
  acc = array_ops.zeros(zeros_shape, grad.dtype)
  if self.outer_context: self.outer_context.Exit()
  - acc._shape = grad.get_shape() # pylint: disable=protected-access
  self.Enter()
  self.AddName(acc.name)
  