BufferHubProducer: don't check user_metadata_size

Now we are using canonical metadata for all BufferHubQueue, it's
actually wrong to enforce user_metadata_size.

Bug: 75962234
Bug: 77655695
Test: buffer_hub_queue-test, buffer_hub_queue_producer-test,
      SurfaceParcelable_test, dvr_buffer_queue-test, libgui_test
Change-Id: I6736ed277f7ac08d1f4a7288ce4a101bc89ca35b