Remove obsolete machine-setup.html reference.

Bug 1231

Change-Id: I629361cf5dddc9d0fbf493e016f1aaf2a50b6935
diff --git a/core/main.mk b/core/main.mk
index 68c1def..5cb160b 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -30,7 +30,7 @@
 $(warning ********************************************************************************)
 $(warning *  You are using version $(MAKE_VERSION) of make.)
 $(warning *  You must upgrade to version 3.81 or greater.)
-$(warning *  see file://$(shell pwd)/docs/development-environment/machine-setup.html)
+$(warning *  see http://source.android.com/download)
 $(warning ********************************************************************************)
 $(error stopping)
 endif