Remove over-broad `jupyter` requirement

https://github.com/conda-forge/lux-widget-feedstock/blob/e7ed7cec7a92a7241c94c342ddd2818611409602/recipe/meta.yaml#L26

I was surprised when installing `lux` pulled in the `qtconsole`. It turns out this is because of the dependency here on the `jupyter` meta-package:
```
jupyter 1.0.0 py_2
------------------
file name : jupyter-1.0.0-py_2.tar.bz2
name : jupyter
version : 1.0.0
build : py_2
build number: 2
size : 4 KB
license : BSD 3-Clause
subdir : noarch
url : https://conda.anaconda.org/conda-forge/noarch/jupyter-1.0.0-py_2.tar.bz2
md5 : 46b26993ed7c689863313a03ee39e5e3
timestamp : 2019-03-26 08:55:20 UTC
dependencies:
- ipykernel
- ipywidgets
- jupyter_console
- nbconvert
- notebook
- python
- qtconsole
```

In the upstream repo the requirement is *only* for the `notebook` rather than the whole `jupyter` package:
https://github.com/lux-org/lux-widget/blob/fd410962395131a70ba482b9510d9ee1313c18a1/setup.py#L85-L88