Ignore ro.adb.secure in user builds.

Require authorization by default, and remove the ability to override
that in user builds. (userdebug and eng are still free to do whatever
they want.)

Bug: http://b/21862859
Change-Id: Ibf8af375be5bf1141c1ad481eee7a59fb10a7adb
diff --git a/adb/adb_auth.h b/adb/adb_auth.h
index 1e1978d..a13604a 100644
--- a/adb/adb_auth.h
+++ b/adb/adb_auth.h
@@ -19,7 +19,7 @@
 
 #include "adb.h"
 
-extern int auth_enabled;
+extern bool auth_required;
 
 int adb_auth_keygen(const char* filename);
 void adb_auth_verified(atransport *t);