BRUSSELS (Reuters) - Greek officials who have been negotiating a debt deal with Athens' creditors left for home on Thursday, a Greek source told Reuters after the IMF said its team had also quit Brussels citing outstanding differences. "They have all left," the source said when asked if any of the Greek officials involved in technical level talks with the so-called Brussels Group of creditor institutions were still present in the city. The institutions are the European Commission, European Central Bank and the International Monetary Fund. ...