Remove flash from kubuntu-restricted-addons?

[Rik Mills]

Ubuntu and other favours did this a while back

https://bugs.launchpad.net/ubuntu/+source/ubuntu-restricted-addons/+bug/1709166

https://launchpad.net/ubuntu/+source/ubuntu-restricted-addons/25

* Drop Adobe Flash as it will be EOL before end of next LTS

I believe we did have some discussion of this at the time, and either
said leave it, or did not make a firm decision.

I think it is appropriate to re-visit this discussion before be go to beta.

Please comment on https://phabricator.kde.org/T8088 if you have an
account, or are willing to get a KDE identity account.