Revert "Enable R8 by default (fifth attempt)"

This reverts commit 1d4e668cf9492c21ab1fa80b1605eb350d9f7b5d.

Reason for revert: b/72373167

Change-Id: I913869aed9061aae8da18165b3a3167a52bad486
(cherry picked from commit ca48094d0394bf52286fa99b60e9f719b0d3e7af)
diff --git a/core/config.mk b/core/config.mk
index 7ed3046..3ed0ea7 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
 
 #