Remove unused source build

kokoro/release/python/linux/build_artifacts.sh

@@ -44,24 +44,3 @@ build_artifact_version 3.4
 build_artifact_version 3.5
 build_artifact_version 3.6
 build_artifact_version 3.7
-
-# Build source package
-
-# Clean up env
-rm -rf venv
-sudo rm -rf protobuf
-git clone https://github.com/google/protobuf.git
-cd protobuf
-git checkout $BUILD_COMMIT
-
-# Make sure all files are world-readable.
-find python -type d -exec chmod a+r,a+x {} +
-find python -type f -exec chmod a+r {} +
-umask 0022
-
-cd python
-
-# Be sure to run build before sdist, because otherwise sdist will not include
-# well-known types.
-python setup.py clean build sdist
-ls