Remove active_buffer_bit_mask_ from BufferNode.

BufferNode already have metadata which contains active_clients_bit_mask,
which serves the same purpose as active_buffer_bit_mask_ but also have
other usage. This change removes the redundant active_buffer_bit_mask_
from BufferNode.

Test: buffer_node-test on marlin-eng and vega_xr build
Bug: 112007999
Change-Id: I7695dc5d6eb84a4a5c73148e9636871cc7776df4