Revert "Enable R8 by default (third attempt)"

Bug: 70858752

This reverts commit 658e4e4e3a975244d078ba3b6332f68486e727bc.

Reason for revert: breaks com.android.systemui.util.leak.LeakDetectorTest#trackInstance_doesNotLeakTrackedObject

which breaks presubmit

Change-Id: I6759cbef6dd5149ddb57836cd080829a5394473d
diff --git a/core/config.mk b/core/config.mk
index c54d119..d317bd0 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -547,7 +547,7 @@
 
 # Default R8 behavior when USE_R8 is not specified.
 ifndef USE_R8
-  USE_R8 := true
+  USE_R8 := false
 endif
 
 #