ATHENS, Greece — Greeks packed city squares for dueling rallies late into the night Friday, as polls showed a dead heat between the ‘yes’ and ‘no’ camps ahead of a bailout referendum Sunday that could be Greece’s most important vote since it joined the European Union. More than 40,000 people gathered at the two rallies, half a mile apart, before Sunday’s vote on whether to accept creditors’ proposals for more austerity in exchange for rescue loans, or reject the deal as a show of defiance against years of harsh economic austerity. “This is not a protest.