block: remove BlockDriver.bdrv_write_compressed

There are no block drivers left that implement the old
.bdrv_write_compressed interface, so it can be removed. Also now we have
no need to use the bdrv_pwrite_compressed function and we can remove it
entirely.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Jeff Cody <jcody@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: John Snow <jsnow@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qemu-img.c b/qemu-img.c
index c2ea494..1090286 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -2034,7 +2034,7 @@
         const char *preallocation =
             qemu_opt_get(opts, BLOCK_OPT_PREALLOC);
 
-        if (!drv->bdrv_write_compressed && !drv->bdrv_co_pwritev_compressed) {
+        if (!drv->bdrv_co_pwritev_compressed) {
             error_report("Compression not supported for this file format");
             ret = -1;
             goto out;