Disable the legacy guard algorithm. Code isn't removed yet.

(Keeping the code around in case I broke Tor in some unexpected
way.)

src/or/entrynodes.h

@@ -31,7 +31,7 @@ typedef struct entry_guard_restriction_t entry_guard_restriction_t;
 /*
   XXXX Prop271 undefine this in order to disable all legacy guard functions.
 */
-#define ENABLE_LEGACY_GUARD_ALGORITHM
+// #define ENABLE_LEGACY_GUARD_ALGORITHM
 
 /* Information about a guard's pathbias status.
  * These fields are used in circpathbias.c to try to detect entry