Clear out old license package name, if any.

Bug: 244574519

Test: m droid dist
Change-Id: I4daa18dc9bdbea30cff3098eca5fc0eb7e5739af
diff --git a/core/notice_files.mk b/core/notice_files.mk
index efc1751..b87215e 100644
--- a/core/notice_files.mk
+++ b/core/notice_files.mk
@@ -11,6 +11,8 @@
 
 ifneq (,$(strip $(LOCAL_LICENSE_PACKAGE_NAME)))
 license_package_name:=$(strip $(LOCAL_LICENSE_PACKAGE_NAME))
+else
+license_package_name:=
 endif
 
 ifneq (,$(strip $(LOCAL_LICENSE_INSTALL_MAP)))