Slurpee Light marks first Slurpee-branded sugar-free drink. 7-Eleven Inc. is  kicking off its “Flavors of Summer” campaign with Slurpee Lite Fanta Sugar-Free Mango, promising all of the flavor of a traditional Slurpee drink with 50% fewer calories. This marks the first Slurpee-branded, sugar-free drink and the first sugar-free frozen beverage to be available at participating…