Docs: remove sphinx_cheatsheet and visual_aids

[ramirezfranciscof]

Fixes #4034 and fixes #4033

The content of visual_aids was moved to the wiki here, the content of the sphinx_cheatsheet was just removed (the wiki already contains a link to an official reference resource). Both files are no longer in the docs.

[csadorf]

Great! Can you make sure that there is a link to the "Graph Easy" wiki page on the "Writing Documentation" wiki page? Otherwise I'm afraid that it will be very hard to find.

[ramirezfranciscof]

@csadorf tis done.

[sphuber]

@ramirezfranciscof I edited your OP to use the keyword "fixes" to mark which issues will be fixed by this. You can see that the word is underlined showing that Github understands that it has special meaning. There are other keywords that you can use like "closing", but the way you wrote it there won't be an automatic link created in the corresponding issues.

[ramirezfranciscof]

@sphuber Hey, why did this not automatically close the corresponding issues? Did github not recognize the "fixes" correctly because they were edited in instead of being in the original OP?

[sphuber]

The reason is just that it wasn't merged into develop but into docs-revamp. Github will only respect those triggers when merging into the "main" branch, which we have set to develop. I guess the philosophy is that until the fix is merged into the main branch it isn't "really" fixed. So I just do it manually for now in order to keep track of what has been done