Fix should_run_npm_install check function

[PytLab]

Should check for package_json file, node_modules dir and npm
installation.

[vidartf]

I'm not sure if I follow the logic here: If the package.json file cannot be found, it should fail with an exception, as clearly something is misconfigured. The node_modules logic seem OK.

[vidartf]

Note: A more modern solution here would be to use a PEP518 type pyproject.toml file, with a build dependency on jupyter_packaging.

[martinRenou]

This code does not exist anymore, let's close this PR