Don't confuse servo assist and ABS - they are two, distinct, exclusive elements of the braking system. Similarly, brake linking is another seperate element that provides a balance of front and rear braking when applying brakes via the front brake lever.
Servo assist is analogous to power brakes. If they fail, you still have brakes, just not assisted - meaning you will need to exert more force on the brakes to stop.
ABS is the anti-lock element to the brakes.
The three are only related in that they are part of the braking system, but are independent features. So, are you looking to eliminate the servo assist, ABS, or linked brakes. I don't believe any are optional, but the creative mind 'could' turn off the ABS, if desired.