Revert "Default NDK modules to libc++_shared."

This reverts commit 6168f5baf1111d9cc6ec3f27d23edc7c53ae3908.

Reason for revert: http://b/70718590

Change-Id: I3e7afe3d1642260c2b5103cb07c636b0b5d72379
diff --git a/core/binary.mk b/core/binary.mk
index c468079..2f306b2 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -187,7 +187,7 @@
   endif
   LOCAL_NDK_STL_VARIANT := $(strip $(LOCAL_NDK_STL_VARIANT))
   ifeq (,$(LOCAL_NDK_STL_VARIANT))
-    LOCAL_NDK_STL_VARIANT := c++_shared
+    LOCAL_NDK_STL_VARIANT := system
   endif
   ifneq (1,$(words $(filter none system stlport_static stlport_shared c++_static c++_shared gnustl_static, $(LOCAL_NDK_STL_VARIANT))))
     $(error $(LOCAL_PATH): Unknown LOCAL_NDK_STL_VARIANT $(LOCAL_NDK_STL_VARIANT))