Howdy
Not an outboard guy but seen this question many times. In searching the net there appears to be two ways, remove it all, and bypass. There are kits out there for removing and most say it is easy and straight forward. The other method is to loop the oil hose to circulate the oil thru the tank only. This way stops the oil injection but the motor doesn't know it.
Hope an OB guy comes along, but I just searched on "Mercury outboard oil tank removal"