Good question because it seems easy to be confused by them.
The rev limit stops you revving too high and damaging the engine or going beyond peak power (because engineers set the limit based on calculations/physics/experience etc)
The speed limit stops you going too fast (for reasons such as tyre rating, gentlemen's agreements, chassis limits like brakes and suspension etc)
If there was no speed limiter, you would rev all the way to redline and the rev limit would limit your speed.
But the rev limiter MUST be there because if the only limiter was the speed one, at 138mph, then you're not going to hit that until 5th & 6th gear, meaning you won't hit the rev limit in those gears because you would hit the speed limit first.
Without rev limiter, you could rev the engine to its death in 1st 2nd 3rd 4th as you wouldn't hit the speed limiter.
If you "remove" the speed limiter i.e. change it from 138mph or whatever up to say 178mph, which is roundabout where you will hit the rev limiter anyway.
You can change it to 200mph but you will not be able to get past 178mph because the rev limit will be hit. Also the bike might not have the power to reach 178 anyway.