Remove patches for catching file browser selected items change

[jtpio]

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Follow-up to https://github.com/jupyter/notebook/pull/6888

https://github.com/jupyter/notebook/pull/6888 added a few patches to be able to know when the file browser selected items change:

https://github.com/jupyter/notebook/blob/fd45f31f983097e1217d4a42488aebef9dfb3d24/packages/tree-extension/src/index.ts#L139-L153

Ideally there should be a built-in signal emitted when this is the case. Tracked upstream in https://github.com/jupyterlab/jupyterlab/issues/14598.

For this issue to be solved https://github.com/jupyterlab/jupyterlab/issues/14598 would first have to be fixed and released in JupyterLab, so Notebook 7 can be updated with the latest versions of the packages.