Remove package obj dir before building

If a file was removed from the source of the rsync and one does an
incremental build the removed file will still be present in obj.

Packages aren't built incrementally by pbuilder so might as well
start from a clean state every build.

Change-Id: I6dc0db5a7dab9de6562e9393b99ed4475f348383
diff --git a/packages.mk b/packages.mk
index 2a91e6a..3320fa8 100644
--- a/packages.mk
+++ b/packages.mk
@@ -63,6 +63,7 @@
 
 	$(ROOTDIR)/build/update_packages.sh
 	cd $(ROOTDIR)/$2; git submodule init; git submodule update;
+	rm -rf $(PRODUCT_OUT)/obj/$1
 	mkdir -p $(PRODUCT_OUT)/obj/$1
 	rsync -rl --exclude .git/ $(ROOTDIR)/$2/* $(PRODUCT_OUT)/obj/$1
 	cp -r $(ROOTDIR)/packages/$1/debian $(PRODUCT_OUT)/obj/$1