When enableEdition() was called with mode == NONE and the dive
was a manually added dive, it would call into MainWindow::
editCurrentDive(), which would in turn call enableEdition(),
however with another mode. Since the only caller of
enableEdition() is now editCurrentDive() anyway, we can
remove that weird code.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>