Remove notebooks-enabled=1 from jupyter.conf

[fh-mthomson]

In the 2024.09.0 Workbench release notes, Jupyter Hub support is being removed, by default:

Added support for Jupyter Notebook 7. (rstudio-pro#6266)
Replaced code server binary with PWB Code Server. PWB Code Server is bundled with the PWB VS Code Extension, so a separate install is no longer required. It is a fork of VS Code 1.93.0. (rstudio-pro#6265)
In VS Code sessions, Workbench now preserves the open directory or workspace on a per-session basis. (rstudio-pro#6491)
Fixed an issue preventing potential data leakage between users in the same browser session. (vscode-server#17)
Disabled Jupyter Notebooks by default on fresh installs of PWB. (rstudio-pro#6269)

Correspondingly, the product default for notebooks-enabled is 0 - docs

Accordingly, I'd propose updating the values in the helm charts to align: https://github.com/search?q=repo%3Arstudio%2Fhelm%20notebooks-enabled&type=code

Impact: We had removed our setting for notebooks-enabled to leverage the default of 0; but, it was still unexpectedly being set to 1, since we're leveraging Posit's Helm charts as a starting point.