Use prebuilt signapk.jar for unbundled branch.

Change-Id: I762b23931042f7ffde829aaf928f54df46a49d78
diff --git a/tools/Android.mk b/tools/Android.mk
index 92603f5..d6badab 100644
--- a/tools/Android.mk
+++ b/tools/Android.mk
@@ -14,11 +14,7 @@
 # limitations under the License.
 #
 
+ifeq ($(TARGET_BUILD_APPS),)
 LOCAL_PATH := $(call my-dir)
-
-# If we're building only unbundled apps, this is the only tool we need.
-ifneq ($(TARGET_BUILD_APPS),)
-include $(LOCAL_PATH)/signapk/Android.mk
-else
 include $(call first-makefiles-under,$(LOCAL_PATH))
 endif