[Tails-dev] Remove "keyboard layout" part in known issues pa…

Hello,
According to this ticket https://labs.riseup.net/code/issues/7912 the
keyboard layout bug is fixed in Jessie.

I remove this part of the known issues page in this branch:
Repo : https://git-tails.immerda.ch/xin/tails/
Branch : knownissues/keyboardlayout
Last Commit : 78c6561323fc69e327d1eb3d36eb46f19371d761

Cheers.
xin