Remove non-working old notebooks

[benjaminleighton]

For now can we remove everything except the subdirectories at https://github.com/rom-py/rompy/tree/main/notebooks? @rafa-guedes and @tomdurrant?

[tomdurrant]

Yes, I think we can. But arguably we should remove all notebook from this repo, and make a separate examples repo (see #61).

[rafa-guedes]

@benjaminleighton I have removed some of the legacy swan ones in #66. There is still some cleanup to be done. Agree with @tomdurrant we could move notebooks into a standalone repo in rom-py organisation to avoid this repo becoming too large.