Removing python headers and Win32 Python2 inits in C++ (#3011)

* Removing python headers and code for Python2 compatibility.

* Restoring python3 inits.

torchvision/csrc/cpu/video/Video.cpp

-
 #include "Video.h"
 #include <c10/util/Logging.h>
 #include <torch/script.h>
@@ -9,22 +8,6 @@
 using namespace std;
 using namespace ffmpeg;
 
-// If we are in a Windows environment, we need to define
-// initialization functions for the _custom_ops extension
-// #ifdef _WIN32
-// #if PY_MAJOR_VERSION < 3
-// PyMODINIT_FUNC init_video_reader(void) {
-//   // No need to do anything.
-//   return NULL;
-// }
-// #else
-// PyMODINIT_FUNC PyInit_video_reader(void) {
-//   // No need to do anything.
-//   return NULL;
-// }
-// #endif
-// #endif
-
 const size_t decoderTimeoutMs = 600000;
 const AVPixelFormat defaultVideoPixelFormat = AV_PIX_FMT_RGB24;
 const AVSampleFormat defaultAudioSampleFormat = AV_SAMPLE_FMT_FLT;

torchvision/csrc/cpu/video/Video.h

@@ -6,7 +6,6 @@
 #include <vector>
 
 #include <ATen/ATen.h>
-#include <Python.h>
 #include <c10/util/Logging.h>
 #include <torch/script.h>
 

torchvision/csrc/cpu/video_reader/VideoReader.cpp

@@ -12,18 +12,11 @@ using namespace ffmpeg;
 // If we are in a Windows environment, we need to define
 // initialization functions for the _custom_ops extension
 #ifdef _WIN32
-#if PY_MAJOR_VERSION < 3
-PyMODINIT_FUNC init_video_reader(void) {
-  // No need to do anything.
-  return NULL;
-}
-#else
 PyMODINIT_FUNC PyInit_video_reader(void) {
   // No need to do anything.
   return NULL;
 }
 #endif
-#endif
 
 namespace video_reader {
 

torchvision/csrc/empty_tensor_op.h

@@ -2,8 +2,6 @@
 
 // All pure C++ headers for the C++ frontend.
 #include <torch/all.h>
-// Python bindings for the C++ frontend (includes Python.h).
-#include <torch/python.h>
 
 class NewEmptyTensorOp : public torch::autograd::Function<NewEmptyTensorOp> {
  public:

torchvision/csrc/vision.cpp

@@ -17,22 +17,13 @@
 #include "nms.h"
 
 // If we are in a Windows environment, we need to define
-// initialization functions for the _C extension
+// initialization functions for the _custom_ops extension
 #ifdef _WIN32
-#if PY_MAJOR_VERSION < 3
-PyMODINIT_FUNC init_C(void) {
-  // No need to do anything.
-  // extension.py will run on load
-  return NULL;
-}
-#else
 PyMODINIT_FUNC PyInit__C(void) {
   // No need to do anything.
-  // extension.py will run on load
   return NULL;
 }
 #endif
-#endif
 
 namespace vision {
 int64_t cuda_version() noexcept {