Fix and enable JarJar in Java builds.

java.mk contained a target to enable JarJar in Java builds, but it was
being bypassed.  This change enabled JarJar as part of the build
process, and fixes a slight bug with the way it was set up.

Change-Id: If24113f399a168939a1a1d0738c5df57caf8d05f
diff --git a/core/config.mk b/core/config.mk
index 82090fa..6ff3d75 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -210,7 +210,7 @@
 MKTARBALL := build/tools/mktarball.sh
 TUNE2FS := tune2fs
 E2FSCK := e2fsck
-JARJAR := java -jar $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
+JARJAR := $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
 PROGUARD := external/proguard/bin/proguard.sh
 JAVATAGS := build/tools/java-event-log-tags.py