Path issue if remove `npm install jupyterlab-plotly` in dockerfile

[grallewellyn]

Ideally, we remove npm install jupyterlab-plotly from the jupyterlab/dockerfile because we already have plotly in the environment.yml and we are trying to extract installs out of the dockerfiles. However, removing it results in Type Error: The "path" argument must be of type string or an instance of Buffer or URL. Received undefined more information here

[grallewellyn]

Sujen suggested removing the jlpm cache clean line to resolve this problem since jupyter lab clean does this for us now