Revert "Enforce that PRODUCT_ variables aren't modified by module makefiles"

This reverts commit 95e743a6c02c9f9844cab95635b4954ecd82e7ff.
diff --git a/core/main.mk b/core/main.mk
index 9efdc5d..8172b22 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -474,7 +474,7 @@
 
 # Before we go and include all of the module makefiles, stash away
 # the PRODUCT_* values so you can't get to them.
-stash_product_vars:=true
+stash_product_vars:=#true
 ifeq ($(stash_product_vars),true)
   $(call stash-product-vars, __STASHED, DO_NOT_USE_IN_ANDROID_MK_)
 endif