[BE] Rectify some references to caffe2 (#140204)

- Rename `tools.build_pytorch_libs.build_caffe2` to `tools.build_pytorch_libs.build_pytorch`
- Delete number of `if BUILD_CAFFE2` conditions

Pull Request resolved: https://github.com/pytorch/pytorch/pull/140204
Approved by: https://github.com/huydhn, https://github.com/r-barnes, https://github.com/atalman

tools/build_pytorch_libs.py

@@ -2,7 +2,6 @@ from __future__ import annotations
 
 import os
 import platform
-import shutil
 from glob import glob
 
 from setuptools import distutils  # type: ignore[import]
@@ -71,7 +70,7 @@ def _create_build_env() -> dict[str, str]:
     return my_env
 
 
-def build_caffe2(
+def build_pytorch(
     version: str | None,
     cmake_python_library: str | None,
     build_python: bool,
@@ -87,8 +86,3 @@ def build_caffe2(
     if cmake_only:
         return
     cmake.build(my_env)
-    if build_python:
-        caffe2_proto_dir = os.path.join(cmake.build_dir, "caffe2", "proto")
-        for proto_file in glob(os.path.join(caffe2_proto_dir, "*.py")):
-            if proto_file != os.path.join(caffe2_proto_dir, "__init__.py"):
-                shutil.copy(proto_file, os.path.join("caffe2", "proto"))