Update docs to remove install command

There is no `jupyter serverextension install` command

Author: dleen

docs/source/nbclassic_dev_faq.rst

@@ -83,5 +83,4 @@ pending to be merged into the `Jupyter-contrib/jupyter_nbextensions_configurator
     $ pip install jupyter_nbextensions_configurator
     $ jupyter nbextension install --sys-prefix --py jupyter_nbextensions_configurator --overwrite
     $ jupyter nbextension enable --sys-prefix --py jupyter_nbextensions_configurator
-    $ jupyter serverextension install --sys-prefix --py jupyter_nbextensions_configurator --overwrite
-    $ jupyter serverextension enable --sys-prefix --py jupyter_nbextensions_configurator
+    $ jupyter serverextension enable --sys-prefix --py jupyter_nbextensions_configurator