Fix connection to KCoreDirLister::redirection() signal

- KCoreDirLister::redirection(const QUrl &, const QUrl &) has been in KIO
for a long time, and both it and the other deprecated redirection(const QUrl &)
signal are emitted by KCoreDirLister, hence no need for the conditional
in the code; spotted by kossebau.

- Call setCurrentDirUrl() directly in the lambda, and drop the now redundant
slotDirListerRedirection() slot.