Remove unused jupyterlab-plotly package

Seems like jupyterlab-plotly doesn't actually exist on conda-forge, and this was included accidentally in 1fa2727?

environment.yml

@@ -42,7 +42,6 @@ dependencies:
   - jupyterlab-git~=0.50.0
   - jupyterlab-h5web~=11.1.0
   - jupyterlab-myst~=2.4.2
-  # - jupyterlab-plotly~=5.18.0 # Outdated according to jupyterlab
   - jupyterlab_pygments~=0.3.0 # To bring extension up-to-date
   - jupytext~=1.16.1
   - nbdime~=4.0.1