Remove demo scripts that duplicate notebooks (#575)

[timpitman]

Over time, StellarGraph has moved to Jupyter notebooks for demos, rather than scripts.

After some discussion, it appears that the demo scripts were generally used for development and debugging, and hence are no longer required. Removing them will remove the need to add them to CI for #575 and will also reduce our code surface for future refactoring, allowing us to concentrate on demo notebooks.

The only script remaining is: demos/node-classification/hinsage - this has no Jupyter notebook equivalent, and also can't be tested on CI due to use of the YELP dataset, and is listed with other untestable notebooks in #818.

[review-notebook-app]

Check out this pull request on 

You'll be able to see Jupyter notebook diff and discuss changes. Powered by ReviewNB.

[codeclimate]

Code Climate has analyzed commit d843e8c and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Security	1

View more on Code Climate.

[codecov-io]

Codecov Report

Merging #889 into develop will decrease coverage by 0.6%.
The diff coverage is 51.7%.

@@            Coverage Diff            @@
##           develop    #889     +/-   ##
=========================================
- Coverage     85.7%   85.1%   -0.6%     
=========================================
  Files           45      49      +4     
  Lines         4901    5014    +113     
=========================================
+ Hits          4200    4266     +66     
- Misses         701     748     +47

Impacted Files	Coverage Δ
stellargraph/core/element_data.py	92.2% <100%> (-0.3%)	⬇️
stellargraph/connector/__init__.py	100% <100%> (ø)
stellargraph/connector/neo4j/__init__.py	100% <100%> (ø)
stellargraph/data/loader.py	54.2% <100%> (+32.2%)	⬆️
stellargraph/connector/neo4j/mapper.py	33.9% <33.9%> (ø)
stellargraph/connector/neo4j/sampler.py	35.6% <35.6%> (ø)
stellargraph/layer/graphsage.py	79.4% <66.7%> (+0.1%)	⬆️
stellargraph/datasets/datasets.py	97.6% <96.3%> (-2.4%)	⬇️
... and 3 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5ec46e6...d843e8c. Read the comment docs.

[kjun9]

Looks good to me 👍

As for the HinSAGE script, I think we should turn that into a notebook as well even if we can't run it in CI?

[PantelisElinas]

If that's what you want to do, then deleting the scripts is fine by me.

[timpitman]

Looks good to me 👍

As for the HinSAGE script, I think we should turn that into a notebook as well even if we can't run it in CI?

#892