Use more variables from Soong

Remove more copies of variables that are computed by Soong.

Test: m checkbuild
Change-Id: If78d4650438cc91d00c691db2fc97c5b790d5648
diff --git a/core/definitions.mk b/core/definitions.mk
index f32a995..d54fd90 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2270,7 +2270,7 @@
 # $(1): the package file we are signing.
 define sign-package-arg
 $(hide) mv $(1) $(1).unsigned
-$(hide) $(JAVA) -Djava.library.path=$(SIGNAPK_JNI_LIBRARY_PATH) -jar $(SIGNAPK_JAR) \
+$(hide) $(JAVA) -Djava.library.path=$$(dirname $(SIGNAPK_JNI_LIBRARY_PATH)) -jar $(SIGNAPK_JAR) \
     $(PRIVATE_CERTIFICATE) $(PRIVATE_PRIVATE_KEY) \
     $(PRIVATE_ADDITIONAL_CERTIFICATES) $(1).unsigned $(1).signed
 $(hide) mv $(1).signed $(1)