block: remove qcow2 .bdrv_make_empty implementation

The QCOW2 .bdrv_make_empty implementation always returns 0 for success,
but does not actually do anything.

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/qcow2.c

@@ -1689,26 +1689,6 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options,
     return ret;
 }
 
-static int qcow2_make_empty(BlockDriverState *bs)
-{
-#if 0
-    /* XXX: not correct */
-    BDRVQcowState *s = bs->opaque;
-    uint32_t l1_length = s->l1_size * sizeof(uint64_t);
-    int ret;
-
-    memset(s->l1_table, 0, l1_length);
-    if (bdrv_pwrite(bs->file, s->l1_table_offset, s->l1_table, l1_length) < 0)
-        return -1;
-    ret = bdrv_truncate(bs->file, s->l1_table_offset + l1_length);
-    if (ret < 0)
-        return ret;
-
-    l2_cache_reset(bs);
-#endif
-    return 0;
-}
-
 static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
     int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
 {
@@ -2252,7 +2232,6 @@ static BlockDriver bdrv_qcow2 = {
     .bdrv_has_zero_init = bdrv_has_zero_init_1,
     .bdrv_co_get_block_status = qcow2_co_get_block_status,
     .bdrv_set_key       = qcow2_set_key,
-    .bdrv_make_empty    = qcow2_make_empty,
 
     .bdrv_co_readv          = qcow2_co_readv,
     .bdrv_co_writev         = qcow2_co_writev,