Remove legacy persistent BufferHub use case

This CL cleans up unused BufferHub code path. The motivation of doing
this is multifold:

1. Reduces future maintainace cost (e.g. when moving to libgui, there
   will be less code to rename and re-style).
2. Removes unnecessary code complexity so that the code base is easier
   and cleaner for future new reader to understand.
3. Prepares future work for supporting standalone GraphicBuffer in
   BufferHub by avoid future logical and naming conflicts between
   legacy PersistentBuffer/Detach/Attach and newly proposed detached
   GraphicBuffer in BufferHub.

Bug: 70046255
Bug: 70912269
Test: buffer_hub-test, buffer_hub_queue-test,
      buffer_hub_queue_producer-test, dvr_api-test, libgui_test

Change-Id: Ie9a0f55e3f620769bac58c81439d840402451b82