Only last executed cell's output is shown on notebook re-open

[3coins]

Steps to reproduce

1. Add 2 cells with some source in a notebook
2. Execute both cells
3. Close the notebook, and open again
4. Only outputs for last executed cell is shown
5. Another issue is that the dirty flag is visible on the notebook, while there are no unsaved changes

[3coins]

@ellisonbg
This statement removes all the saved outputs for the notebook by removing the full directory for the file_id for every cell execution which is causing the above issue. Was this an intentional change?
https://github.com/ellisonbg/jupyter-rtc-core/blob/d78b852149908bf15922d78c40f2a8fd5b681fc9/jupyter_rtc_core/outputs/output_processor.py#L128

[ellisonbg]

That is an mistake, that statement can be removed.

[Zsailer]

Fixed in #70