Investors have had enough of Europe. Amid a global selloff that has sent the Standard & Poor’s 500 Index down 5.2 percent in three weeks, losses have been almost twice as big in the Euro Stoxx 50 Index, where last week’s 4.5 percent retreat was the largest since 2012. A record $1 billion was withdrawn from an exchange-traded fund tracking Europe in the period as Mario Draghi, the central-bank president, warned of signs the recovery is losing momentum.