Remove BufferNode in libbufferhubd

DetachedBuffer used to need BufferNode as its component, but now it is
renamed to BufferHubBuffer and refactored with hwbinder backend, so
there is no need to keep a BufferNode dependency in libbufferhubd.

Test: buffer_hub-test
Bug: 118891412
Change-Id: I80dde2eed788b3bd4fd1f8148e74526bff248f06