By Jose Torres TAPACHULA, Mexico (Reuters) – Hundreds of migrants set off from Mexico’s southern border early on Friday on a northward journey to the U.S.-Mexico border where hundreds of others are stranded following a deal to expel Venezuelan migrants crossing into the United States. The group of people departed around 4 a.m. from the city of Tapachula, near Mexico’s border with Guatemala, en route to San Pedro Tapanatepec in Mexico’s Oaxaca state, where migrants can acquire permits to cross the country. A migration official estimated the total number of migrants at 500, mostly Venezuelans, a…