This amount cannot be removed from your project page, but donors can easily exclude it in the donation step. Any donor can opt out of including it in the checkout process - if someone selects "give" on your project page, they can click "edit" or "optional donation" in the cart review step of the donation process and opt out.
The optional donation supports the labor performed by DonorsChoose.org to turn your donation into a live project. DonorsChoose.org ensures "end to end" integrity on every student project by reviewing project submissions, procuring materials, verifying school shipping addresses and maintaining contact with the teacher and other school officials throughout the process. It is definitely essential to keep DonorsChoose.org going!