Do not use storage_client in CMake. (googleapis/google-cloud-cpp-spanner#66)
Do not use storage_client in CMake. (googleapis/google-cloud-cpp-spanner#66)

I forgot to clean this up, we no longer need the `storage_client` to
compile the code.
googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp