I hope you plan to remove the code that manages the circular buffer too. You're asking for trouble if you try to step on the library's toes.
Besides, what does it mean "I don't need the circular buffer" ?
My strong suggestion is just leave the library code alone. It's there for a purpose. If you think you know better than whoever wrote the library, just don't use it and write you own code.
OTOH, if you need to manage serial received data there are plenty of examples around, and many helpful people around here. Just show what you have and ask for hints.
The path you're on isn't taking you anywhere IMHO.