qt: remove unnecessary comment

Qt in buildroot should not depend on dbus installed on build platform,
if so this is (or was) a bug in buildroot.

Looks like that this note is left over from ancient buildroot days,
so remove it.

Signed-off-by: Michael Roth <mroth@nessie.de>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>