The lastUsedDir() functions of MainWindow and Smrtk2ssrfcWindow don't
use any member-objects and are only used in their respective translation
units. Therefore, remove them from the class and made of static linkage.
The lastUsedImageDir() function was declared as a slog, which makes
no sense. Make it a normal static function (though one might argue
why it is assiociated with the DiveListView class in the first place).
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
4e8079f527