Hartson was a long snapper signed to a reserve / futures contract with the Chiefs at the start of the offseason in January. He went undrafted in 2013 before spending some time with the Bears.
Along with Hartson, James Winchester and Jorgen Hus, the Chiefs had three long snappers on the roster. You knew there was no chance they would carry more than one long snapper so moves would eventually be made. What's not clear is why the Chiefs could make this move now. There were no practices between the time Hartson was signed and when he was cut. The Chiefs can have 90 players on the offseason roster so they had roster space (unless they plan on signing a dozen players very soon).
The Chiefs will have a new long snapper for the first time in seven years in 2015 with Thomas Gafford leaving via free agency.