Delete Tensor::swap(), replace with pointer swap (pytorch#12730)

Summary:
Pull Request resolved: pytorch#12730

i-am-not-moving-c2-to-c10

Reviewed By: smessmer

Differential Revision: D10415430

fbshipit-source-id: 8a2ce8611c5fa77bbbd73fb6788c1baa3b370f07

caffe2/core/tensor.h

@@ -311,14 +311,6 @@ class CAFFE2_API Tensor final {
     return ss.str();
   }
 
-  // NB: a.swap(b) is not equivalent to std::swap(a, b);
-  // swap method swaps the CONTENTS of the tensors, while std::swap
-  // swaps the POINTERS.
-  void swap(const Tensor& other) const noexcept {
-    // NB: use get() to get a non-const pointer!
-    std::swap(*impl_.get(), *other.impl_.get());
-  }
-
   void ShareData(const Tensor& src) const {
     impl_.get()->ShareData(*src.impl_.get());
   }

caffe2/utils/filler.h

@@ -27,7 +27,7 @@ class TensorFiller {
     CAFFE_ENFORCE_LE(min, max);
 
     Tensor temp_tensor(shape_, Context::GetDeviceType());
-    tensor->swap(temp_tensor);
+    std::swap(*tensor, temp_tensor);
     Type* data = tensor->template mutable_data<Type>();
 
     // select distribution