Revert "Enable R8 by default (fourth attempt)"

This reverts commit a7e1f925338d09482df5af3f92f74edd67b5979b.

Reason for revert: R8 seems to be a reason for b/72218788.

Change-Id: Ia2f12775b37537cb21036c4bdd5504af8344e830
diff --git a/core/config.mk b/core/config.mk
index ef2cc62..f347109 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -556,7 +556,7 @@
 
 # Default R8 behavior when USE_R8 is not specified.
 ifndef USE_R8
-  USE_R8 := true
+  USE_R8 := false
 endif
 
 #