Revert "Enable R8 by default (sixth attempt)"

This reverts commit 52dd2f8f8ed531afd0e5ee0369a357b0e384f6d1.

Reason for revert: Build failure for NexusLauncherRelease

Change-Id: I4bec5dd1842f78ec1905a99d1338dc0e2dd20aca
diff --git a/core/config.mk b/core/config.mk
index 20acf34..63ccbda 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
 
 #