Remove bogus call and comment from addressbook

QMap::empty() does not empty the list but is the STL
version to ask if the map is empty. Remove the comment
and code as operator>> of QDataStream will clear the
map.

Fixes Coverity CID#89073

Change-Id: I259e518b44afd42b698368b42aedcc3b84240aca
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>