Updated FAQ (google#9671)

FAQ was wrongly listed as a "parent" page, so it ended up with a
mysterious, empty table of contents at the bottom of the page (not to be
confused with the table of contents for the structure of the page itself
which should be there and is left unchanged).

Go to [the current faq page](https://google.github.io/oss-fuzz/faq/) and
scroll to the bottom to see what I mean. This fix cleans that up and I
confirmed by running locally.

docs/faq.md

@@ -1,7 +1,6 @@
 ---
 layout: default
 title: FAQ
-has_children: true
 nav_order: 7
 permalink: /faq/
 ---