WASHINGTON (Reuters) - The U.S. State Department on Wednesday advised U.S. citizens to delay or cancel unnecessary travel to mainland Honduras  due to ongoing political protests and the potential for violence.  The travel alert, which the department said in a statement expires on Dec. 31, follows a dispute over the result of a Nov. 26 presidential election that has sparked deadly protests and a night-time curfew in the poor, violent Central American country.    