Revise the FAQ page at Wiki to keep content up-to-date

[BrutalCoding]

I stumbled upon this FAQ document. I briefly went through it and noticed two things:

1. It was last updated in 2018.
2. The bottom paragraph refers to an issue that was completed years ago.

For example, I think we can remove the entire "Why did the formatter only format some of my code?" section.

I wanted to update it, but it seems that GitHub Wiki is not part of the same source code as the main repo. I can clone the wiki but creating a PR is not possible AFAIK. Anyways, that's a different issue and not related to Dart.

The document is from @munificent and I have mentioned him in that outdated issue too, but opening this issue is probably a safer bet.

[munificent]

This is fixed now, thanks!