Delete TensorImpl::GetDevice() (#20025)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20025

Delete TensorImpl::GetDevice() and clean all its call sites.

Reviewed By: ezyang

Differential Revision: D15170917

fbshipit-source-id: b6862b74aa036198544f79d18a8c0f995cb0ca7b
diff --git a/c10/core/TensorImpl.h b/c10/core/TensorImpl.h
index 3a80a79..907834c 100644
--- a/c10/core/TensorImpl.h
+++ b/c10/core/TensorImpl.h
@@ -972,15 +972,6 @@
   }
 
   /**
-   * The device of a Tensor; e.g., Device(kCUDA, 1) (the 1-index CUDA
-   * device).
-   */
-  Device GetDevice() const {
-    // See NOTE [c10::optional operator usage in CUDA]
-    return *device_opt_;
-  }
-
-  /**
    * @brief Extends the outer-most dimension of this tensor by num elements,
    * preserving the existing data.
    *
diff --git a/caffe2/core/tensor.h b/caffe2/core/tensor.h
index 152fae8..f65e771 100644
--- a/caffe2/core/tensor.h
+++ b/caffe2/core/tensor.h
@@ -172,7 +172,7 @@
   }
 
   at::Device GetDevice() const {
-    return impl_.get()->GetDevice();
+    return impl_.get()->device();
   }
 
   /**