integration wip: use default value for baseUrl

baseUrl defaults to entrypoint.js url so no need to set it explicitly.

On top of that, setting it here would require hosting page to define
global variable accessible from entrypoint.js to configure baseUrl value
for a given environment which:
- adds additional configuration step for hosting page,
- breaks r.js optimizer as it requires call to requirejs.config
to be parsable as JSON.