This removes the feature "SlashCommandEducator" (including test and the png it used to display).

It triggered whenever someone wrote for example .close or !close or ?close, educating the user about having to write /close instead. It was a crucial feature when Discord just introduced slash commands, but now people know about it already.

Why

The problem in practice was that it has a lot of false positives, for example people in casual chat writing about .NET or similar. After reviewing all occurences the last years, almost all of them have been false positives. The feature, right now, causes more annoyance than it helps.

So we decided to remove it all together. An alternative would have been to tweak it to only trigger inside help-threads instead of all channels. But ultimately the need for the feature is kinda gone, so lets just get rid of it.