Remove WindowsTorchApiMacro.h in favor of Export.h (pytorch#69585)

Summary:
Follow up to pytorch#68095

This also changes the files from the ATen folder to include c10's `Export.h` instead since they can't ever be exporting `TORCH_PYTHON_API`.

cc pietern mrshenli pritamdamania87 zhaojuanmao satgera rohan-varma gqchen aazzolini osalpekar jiayisuse SciPioneer H-Huang

Pull Request resolved: pytorch#69585

Reviewed By: mrshenli

Differential Revision: D32958594

Pulled By: albanD

fbshipit-source-id: 1ec7ef63764573fa2b486928955e3a1172150061

Author: peterbell10

BUILD.bazel

@@ -524,7 +524,6 @@ cc_library(
     name = "aten_headers",
     hdrs = [
         "torch/csrc/Export.h",
-        "torch/csrc/WindowsTorchApiMacro.h",
         "torch/csrc/jit/frontend/function_schema_parser.h",
     ] + glob([
         "aten/src/**/*.h",

aten/src/ATen/SequenceNumber.h

@@ -1,7 +1,7 @@
 #pragma once
 
 #include <cstdint>
-#include <torch/csrc/WindowsTorchApiMacro.h>
+#include <c10/macros/Export.h>
 
 namespace at {