Remove outdated FAQ sections

Removes two FAQ sections that were outdated: Ceylon 1.0 was released, and we do have a `final` annotation.

[known-issues.md](https://github.com/ceylon/ceylon-lang.org/blob/deb33cc326562e98845754fcf2a155b5890d56dd/documentation/1.0/faq/known-issues.md) is also severely outdated, but I’m not sure what do do with it. Should we just point users to the issue trackers? Generate a list of issues tagged “BUG” with milestones 1.1 or 1.2? (Those two will be easier to achieve after the OBR merge.) Add the most serious/notable bugs by hand? Remove it completely?