Cleanup .appveyor.yml file
Cleanup .appveyor.yml file

We currently do not need python-appveyor-demo files for appveyor
builds. The installer has bugs. Remove it (and related lines).
If required, it might be easier to write our own Python installer
in the future than to debug these ones.

Bug: T191188
Change-Id: I89cc9e72260ca5a4d9854b756ece6b0585d5ecc7

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core