Remove migration note about selection widgets and dictionaries, now that we reverted the change.
Remove migration note about selection widgets and dictionaries, now that we reverted the change.

Follows up on #3557 to correct the docs
ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets