It is this command: ^$
But sometimes this doesn't work. Because the above mentioned command actually deletes a paragraph and not a line.
What to do in a case like this one:
Marco Borsato
Wat is mijn hart
De Dijk
Niemand in de stad
The above mentioned command doesn't work and doesn't erase the line between the two texts.
What you need to do, is to clear formatting.
Also make sure that after clearing lines, there are no spaces left at the beginning of the lines.