Logged-in user language preferences were broken in commit 9ca6bb55

.
This change removes caching on the session and config languages, which
are quick to retrieve anyway, but leaves it in place for the user
language preference and locale setting.

Change-Id: Ib601f2227409bbbc63d269fe079915cc0e902fc2
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>