block: Remove qemu_root_bds_opts

The remaining options in qemu_root_bds_opts (aio and copy-on-read)
aren't used any more, the QAPI schema doesn't contain them. Therefore
all the code processing qemu_root_bds_opts options is dead and can be
removed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>