Commit 1b7fd729559c ("block: rename buffer_alignment to
guest_block_size") noted:
At this point, the field is set by the device emulation, but completely
ignored by the block layer.
The last time the value of buffer_alignment/guest_block_size was
actually used was before commit 339064d50639 ("block: Don't use guest
sector size for qemu_blockalign()").
This value has not been used since 2013. Get rid of it.
Cc: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>