chore(request-node): remove dockerfile

[alexandre-abrioux]

Description of the changes

This PR is a proposal to remove the Dockerfile from the request-node package as it could bring some confusion (explanation bellow).

1/ Prod Releases

The Dockerfile is not used for production releases anymore since this responsibility was migrated to the RequestNetwork/docker-images repository.

2/ Pre Releases

Pre-production releases are now also handled by the RequestNetwork/docker-images repository.

3/ Dev Builds

The Dockerfile was still useful for development builds.

The main issue is that, when internal dependencies are modified locally, for instance @requestnetwork/ethereum-storage, the line RUN npm install would still pick the latest release of those packages on NPM instead of locally changed ones.

That is why a Dockerfile.dev now exists in the package to take care of this use case.

Overall it looks to me like this Dockerfile is not needed anymore and can bring some confusion to new contributors.

[coveralls]

Coverage remained the same at 89.449% when pulling 139ad38 on request-node-dockerfile into f540b1a on master.