By Paulo Prada and Maria Pia Palermo RIO DE JANEIRO (Reuters) – Brazilian presidential candidate Marina Silva vowed on Thursday to de-politicize regulatory agencies that she says do more to win favor with government allies than ensure fair and efficient markets in Latin America’s biggest economy. Silva, who is running neck-and-neck with President Dilma Rousseff in polls ahead of next month’s election, accused the ruling Workers’ Party of undermining regulation by stacking government watchdogs with party members and allies during its 12 years in power. …