Fixed matplotlib issues in asymmetric well.

[Taylor-96]

Fixed issue with lines.clear() as in quantum well notebooks. Also fixed problem with popping last artist in axis object. Workaround was to use the following approach in order to remove last 3 mu points.

 for artist in (ax3.collections+ax3.lines):
        if isinstance(artist, plt.Line2D) and len(artist.get_xdata()) == 1:
            artist.remove()

[github-actions]

👈 Launch a Binder on branch osscar-org/quantum-mechanics/asymmetric_well_review