AbstractDataFileDialog: deleteLater models

[kif]

Addresses this bug in pyFAI-calib2:
silx-kit/pyFAI#2422

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[kif]

With this PR, I am really outside my comfort zone ...

[t20100]

@kif, I don't remember, was this fixed in another way?

[kif]

This bug is clearly related to PyQt5 where objects are deleted in the wrong order. It is not fixed in pyFAI because it uses this specific silx class. What occurs is that pyFAI-calib2 crashes randomly when using this file-dialog on steroids: the object gets deleted on the python side then Qt tries to access it (to delete it) and it no more exists. It is related to the tree model underneath, something like that. on the one hand, I have never seen the bug with PySide6, on the other, I know this workaround partially works but it is neither a silver-bullet.