Revert "Enable D8 by default."

Breaks EmulatorSmokeTests

Bug: 67569208

This reverts commit 4c1a09823c5b8ee7c976c3e1fa2dad794793a63c.

Change-Id: I85b28b9b59226f4ce6fda0ea2445933eade07d89
diff --git a/core/config.mk b/core/config.mk
index ccd7663..566faae 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -512,7 +512,7 @@
 USE_PREBUILT_SDK_TOOLS_IN_PLACE := true
 
 # USE_D8_BY_DEFAULT is the default behavior, use USE_D8 to override.
-USE_D8_BY_DEFAULT := true
+USE_D8_BY_DEFAULT := false
 ifndef USE_D8
   USE_D8 := $(USE_D8_BY_DEFAULT)
 endif