qt: remove commercial license option

It looks like that nobody is using the commercial license option
because the code is broken (BR2_QT_COMMERCIAL_PASSWORD typo) and
dist.trolltech.com became silent long ago and nobody complained about.

So remove the broken and unused stuff.

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>