There's no legal requirement to have an airbag fitted, however -
1. You'd be a plank to remove a potentially life saving piece of safety equipment.
2. If you do, you'll need to fool the ECU that the airbag is still there - good quality kits come with a resistor complete with the correct connector to plug in place of the airbag.
3. Your insurers will want to know about it - good luck on any personal injury claims if you don't declare and have an accident!