Remove cuda.list from apt sources (protocolbuffers#9896)

This will fix the collect_all_artifacts.sh script, which was broken
recently when NVidia stopped publishing Cuda packages for Ubuntu 16.04.

kokoro/release/collect_all_artifacts.sh

@@ -50,6 +50,9 @@ cp ${INPUT_ARTIFACTS_DIR}/build64/src/protoc protoc/macosx_x64/protoc
 # TODO(jtattermusch): use "mono:5.14" docker image instead so we don't have to apt-get install
 sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
 echo "deb https://download.mono-project.com/repo/ubuntu stable-xenial main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
+# NVidia has stopped publishing Cuda packages for Ubuntu 16.04, so we need to
+# delete this file to allow the apt update to run successfully.
+sudo rm -f /etc/apt/sources.list.d/cuda.list
 sudo apt update
 sudo apt-get install -y nuget