Revert "Use dx.jar directly"

This reverts commit e37a3c959a833b9979f7e820cb037711c7453c16.

Reason for revert: breaks art test runner

Change-Id: Ice0cd3020ddec7f31eb789867a45f047a75a05d0
diff --git a/core/definitions.mk b/core/definitions.mk
index d0f6d4c..fe8d644 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2557,7 +2557,7 @@
 @echo "target Dex: $(PRIVATE_MODULE)"
 @mkdir -p $(dir $@)
 $(hide) rm -f $(dir $@)classes*.dex
-$(hide) $(DX) \
+$(hide) $(DX_COMMAND) \
     --dex --output=$(dir $@) \
     --min-sdk-version=$(call codename-or-sdk-to-sdk,$(PRIVATE_DEFAULT_APP_TARGET_SDK)) \
     $(if $(NO_OPTIMIZE_DX), \