message: Make the Tensor move constructor actually move the shape member.
  This fixes a ClangTidy warning in "tensor.h". Previously, we accessed the shape member via the `Tensor::shape()` method, which returns an immovable const reference to a `TensorShape`.
diff: @@ -916,7 +916,7 @@ inline Tensor::Tensor(const Tensor& other)
  }
  inline Tensor::Tensor(Tensor&& other)
  - : shape_(std::move(other.shape())), buf_(other.buf_) {
  + : shape_(std::move(other.shape_)), buf_(other.buf_) {
  other.buf_ = nullptr;
  }
  