block: remove QED .bdrv_make_empty implementation

The QED .bdrv_make_empty() implementation does nothing but return
-ENOTSUP, which causes problems in bdrv_commit().  Since the function
stub exists for QED, it is called, which then always returns an error.

The proper way to not support an optional driver function stub is to
just not implement it, so let's remove the stub.
Signed-off-by: NJeff Cody <jcody@redhat.com>
Reviewed-by: NBenoit Canet <benoit@irqsave.net>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/qed.c

@@ -731,11 +731,6 @@ static int64_t coroutine_fn bdrv_qed_co_get_block_status(BlockDriverState *bs,
     return cb.status;
 }
 
-static int bdrv_qed_make_empty(BlockDriverState *bs)
-{
-    return -ENOTSUP;
-}
-
 static BDRVQEDState *acb_to_s(QEDAIOCB *acb)
 {
     return acb->common.bs->opaque;
@@ -1617,7 +1612,6 @@ static BlockDriver bdrv_qed = {
     .bdrv_create              = bdrv_qed_create,
     .bdrv_has_zero_init       = bdrv_has_zero_init_1,
     .bdrv_co_get_block_status = bdrv_qed_co_get_block_status,
-    .bdrv_make_empty          = bdrv_qed_make_empty,
     .bdrv_aio_readv           = bdrv_qed_aio_readv,
     .bdrv_aio_writev          = bdrv_qed_aio_writev,
     .bdrv_co_write_zeroes     = bdrv_qed_co_write_zeroes,