oh dear... dont do it
Nitro mors is the best action here
In general... single pack ( rattle cans) are no good for areas that are going to be constantly in contact ( bike tank) and damaged by fuel ( bike tank )
If it was painted properly, by a pro, he would add a matting agent to the 2 pack clear coat ( ratios depend on paint system) which would harden to a matt or satin finish depending on the ratio.
I guess the nearest your going to get is to as some one said - buff it down with an old grey scotch pad or summit.
then again... If you can get the insides of a computer case powdercoated black for about 50 notes... see about getting your tank done - it will give the finish you want, will be as hard as chuck norris and be cheap as chips
***EDIT***
On a second note some of you are mentioning durability, as in how resistant it is to contact i would imagine?
The type of paints in question suffer more from things like spilled fuel, natural oil from hands and skin and other 'chemicals' and such . . not just scratches and scrapes.
I had to re-spray a fuel tank for a friend who painted it in matt 'bbq paint' and oh my god what a mess !!