Diesel Exhaust Fluid (DEF) is a non-hazardous solution, which is 32.5% urea / 67.5% de-ionized water. DEF is sprayed into the exhaust stream of diesel vehicles to break down dangerous NOx emissions into harmless nitrogen and water. Just fill up DEF when the vehicle tells you to. DEF is widely used on various diesel vehicles including other Mercedes vehicles and across the trucking community.
The start warnings only occur if you ignore the warnings and don't refill DEF or you decide to cheap out and full DEF tank with water or old expired DEF. Since its part of the emissions control system, deleting DEF (if it was possible) would increasing your vehicles pollution and likely make the vehicle non compliant when you needed to get it smogged.
Also in the emissions control system, is the Diesel Particulate Filter (DPF) and there is a separate process shown on the video above that burns off diesel particulates on a regular basis. First burn is a little scary since when the vehicle is new, there is considerable odor from the vehicle as "new stuff" is heated for the first time. Subsequent burns and no big deal and you really only can tell anything happened from the "tink" "tink" "tink" noise from the exhaust system posts burn as it cools down. Just consider your surroundings (long dry grass) if your DPF is full
DEF = Sprayed in the exhaust to reduce NOX.
DFP = Burnt off on a regular basis.