Replace DX_ALT_JAR with USE_D8

Which would invoke the d8 script instead of calling javac on the jar.

BUG: 65212022
Test: m USE_D8=true
Change-Id: I8ee0b14210cb40895b0b208a01606e10a41f0acf
diff --git a/core/config.mk b/core/config.mk
index f74f5b4..d5f3ec2 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -513,13 +513,13 @@
   SIGNAPK_JNI_LIBRARY_PATH := $(HOST_OUT_SHARED_LIBRARIES)
   ZIPALIGN := $(HOST_OUT_EXECUTABLES)/zipalign
 
-  ifndef DX_ALT_JAR
-    DX := $(HOST_OUT_EXECUTABLES)/dx
-    DX_COMMAND := $(DX) -JXms16M -JXmx2048M
+  ifeq ($(USE_D8),true)
+    DX := $(HOST_OUT_EXECUTABLES)/d8
   else
-    DX := $(DX_ALT_JAR)
-    DX_COMMAND := $(JAVA) -Xms16M -Xmx2048M -jar $(DX)
+    DX := $(HOST_OUT_EXECUTABLES)/dx
   endif
+  DX_COMMAND := $(DX) -JXms16M -JXmx2048M
+
 else # TARGET_BUILD_APPS || TARGET_BUILD_PDK
   AIDL := $(prebuilt_sdk_tools_bin)/aidl
   AAPT := $(prebuilt_sdk_tools_bin)/aapt