[People walk through fields after they were sent out during a police operation to evacuate a makeshift camp at the Greek-Macedonian border near the village of Idomeni]By Lefteris Papadimas and Angeliki Koutantou IDOMENI, Greece (Reuters) - Greece has sent in police and bulldozers to clear out Europe's biggest refugee camp because of the deteriorating humanitarian conditions there, but the operation should also unblock a vital artery for the ailing economy. The Idomeni camp, recently home to as many as 8,000 migrants and refugees, had spread out across a railway track on the Macedonian border, choking off Greece's main rail route to the rest of Europe. It has also complicated the privatisation of the country's rail freight business, a condition of its international bailout.