Remove npm-scope for @nuxeo from slave's .npmrc file

Right now, the slave's .npmrc file binds the @nuxeo scope to mavenin via @nuxeo:registry=https://mavenin.nuxeo.com/nexus/repository/npmjs-nuxeo/. However, this makes it harder to publish @nuxeo scoped packages to different registries, since this configuration overrides the --registry=... cli option during publish. As a consequence, in order to publish to the public registry and mavenin, we need to do the following:

npm config set @nuxeo:registry https://mavenin.nuxeo.com/nexus/repository/npmjs-nuxeo/
npm publish
npm config set @nuxeo:registry https://registry.npmjs.org/
npm publish --access public
npm config set @nuxeo:registry https://mavenin.nuxeo.com/nexus/repository/npmjs-nuxeo/

However, this might create some issues in the rare event of two or more concurrent jobs trying to install/publish npm packages at the same time. Removing the @nuxeo:registry=https://mavenin.nuxeo.com/nexus/repository/npmjs-nuxeo/ from the npm config file will allow the --registry to be used to publish to different registries:

npm publish --registry=https://mavenin.nuxeo.com/nexus/repository/npmjs-nuxeo/
npm publish --access public --registry=https://registry.npmjs.org/