Remove BufferHubBuffer:Poll function

In the new eventFd design, BufferHubBuffer will only provide with the
eventfd itself, and user can decide what to do with it. Therefore, the
Poll function is not needed any more.

Test: BufferHub_test, GraphicBuffer_test
Bug: 118891412
Change-Id: I5f5ff71bcedc20de81f246764e878d81b0768eb1
2 files changed