Remove white stroke from traffic signals in Refill icons

[nvkelso]

To solve for tangrams/cinnabar-style#53 the original artwork in the Refill icon set should remove the white stroke on the traffic signal sprite. It looks to be the only icon with that white stroke which makes it discongruous. The Refill icons are then used by Cinnabar, so both Refill and Cinnabar map styles should then be updated with the new spritesheet.