Fix faq menu rendering glitch in docs.s.o

It's glitchy as described in the screenshot [1] When focusing on the faq, the faq is unfolded at the top of the menu but still selected below... It's also not consistent with other behavior of the menu entries.

I've tried multiple things to no avail:

• split the faq/index.rst into multiple faq/.rst
• keep an faq/index.rst and a faq/faq.rst separated
• drop the redundant entry in the main page...
• ...

I'm obviously missing something to actually fix properly. So there, please someone, fix it ;)

Note: there is most likely the same issue in the users doc.

• [1]

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Migrated from T3657 (view on Phabricator)