Remove install of Python 3.9 (#2392)

Author: sampathweb

.kokoro/github/ubuntu/gpu/build.sh

@@ -3,8 +3,6 @@ set -x
 
 cd "${KOKORO_ROOT}/"
 
-sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.9 1
-
 PYTHON_BINARY="/usr/bin/python3.9"
 
 "${PYTHON_BINARY}" -m venv venv