leave them alone, or do what you want.
andrew
since you are asking again, I'll give this an answer. You may like it, or you may not.
There is no manufacturer in the world who is going to sell a product requiring you to remove a piece of a glued-on component. There is no manufacturer in the world who is going to expect people to remove a portion of a multi layered component. If, for any conceivable reason, I am proven wrong, then the manufacturer will have given explicit instructions in writing, and the to-be-removed piece will be visibly different and easily separable. That is my assessment of how companies run things once they get past the initial beginner's stage.
The manufacturer made a sandwich of OSB and rubber. This is just as good as having rubber on the bottom, in terms of its ability to absorb vibration and noise. It may also be good in another way, since it may allow you to slide the tub into position more easily than if the rubbbery piece were on the bottom. This may explain why the layers were built in this order. This is my conjecture and hypothesis.
You can lower the tub by removing a piece of OSB off of the feet too. It's no loss. There is a small risk, which you alone can manage, in terms of getting a smooth surface after unsticking a glued-on layer. No big risk. It may also be better to do this: if there is ever a wet floor under the tub, then the rubbery layer may be thick enough to prevent the OSB above it from sucking up moisture. OSB once wet starts to swell up and self-destruct.
Hope this helps. Don't bite me if you didn't want this kind of answer.
David