NPM can cause issues when running in docker containers, such as:
- requiring write access to the root filesystem and printing a large
annoying warning if it doesn't have it
- not passing signals on to process it starts, making it take longer to
gracefully kill containers
Now that all our Docker images have their own `start` and `download`
scripts to serve as more reliable entrypoints, we can remove all calls
to `npm` by the `pelias` script.
Connects https://github.com/pelias/pelias/issues/745