>> Faster than rsync
cd folder_to_delete
# perl -e 'for(<*>){((stat)[9]<(unlink))}'

>> Other options:
cd folder_to_delete
find . -type f -exec rm -f {} \;

folder_to_delete
for i in $(echo *); do echo "Deleting : $i"; rm -f $i; done

rsync -av --delete /path/empty_dir /path/folder_to_delete