It is only necessary to clear block-obj-y because Makefile.objs
uses "+=" instead of "="; fix that and remove the assignment.
The other variables need not be cleared at all.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Makefile.objs   | 2 +-
 Makefile.target | 3 ---
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/Makefile.objs b/Makefile.objs
index acc53aa..31a84b7 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -13,7 +13,7 @@ authz-obj-y = authz/
 #######################################################################
 # block-obj-y is code used by both qemu system emulation and qemu-img
 
-block-obj-y += nbd/
+block-obj-y = nbd/
 block-obj-y += block.o blockjob.o job.o
 block-obj-y += block/ scsi/
 block-obj-y += qemu-io-cmds.o
diff --git a/Makefile.target b/Makefile.target
index a458506..441ace6 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -175,9 +175,6 @@ endif # CONFIG_SOFTMMU
 dummy := $(call unnest-vars,,obj-y)
 all-obj-y := $(obj-y)
 
-block-obj-y :=
-common-obj-y :=
-chardev-obj-y :=
 include $(SRC_PATH)/Makefile.objs
 dummy := $(call unnest-vars,.., \
                authz-obj-y \
-- 
1.8.3.1