Don't immediately count cannibalized circs as used.

Since they use RELAY_EARLY (which can be seen by all hops on the path),
it's not safe to say they actually count as a successful use.

There are also problems with trying to allow them to finish extending due to
the circuit purpose state machine logic. It is way less complicated (and
possibly more semantically coherent) to simply wait until we actually try to
do something with them before claiming we 'used' them.

Also, we shouldn't call timed out circuits 'used' either, for semantic
consistency.

src/or/circuitbuild.c

@@ -823,9 +823,6 @@ circuit_send_next_onion_skin(origin_circuit_t *circ)
 
       /* We're done with measurement circuits here. Just close them */
       if (circ->base_.purpose == CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT) {
-        /* If a measurement circ ever gets back to us, consider it
-         * succeeded for path bias */
-        circ->path_state = PATH_STATE_USE_SUCCEEDED;
         circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_FINISHED);
       }
       return 0;
@@ -3140,9 +3137,7 @@ circuit_extend_to_new_exit(origin_circuit_t *circ, extend_info_t *exit)
     return -1;
   }
 
-  /* Set timestamp_dirty, so we can check it for path use bias */
-  if (!circ->base_.timestamp_dirty)
-    circ->base_.timestamp_dirty = time(NULL);
+  // XXX: Should cannibalized circuits be dirty or not? Not easy to say..
 
   return 0;
 }

src/or/circuituse.c

@@ -668,18 +668,6 @@ circuit_expire_building(void)
           circuit_build_times_set_timeout(&circ_times);
         }
       }
-
-      if (TO_ORIGIN_CIRCUIT(victim)->has_opened &&
-          victim->purpose != CIRCUIT_PURPOSE_PATH_BIAS_TESTING) {
-        /* For path bias: we want to let these guys live for a while
-         * so we get a chance to test them. */
-        log_info(LD_CIRC,
-                 "Allowing cannibalized circuit %d time to finish building "
-                 "as a pathbias testing circ.",
-                 TO_ORIGIN_CIRCUIT(victim)->global_identifier);
-        circuit_change_purpose(victim, CIRCUIT_PURPOSE_PATH_BIAS_TESTING);
-        continue; /* It now should have a longer timeout next time */
-      }
     }
 
     /* If this is a hidden service client circuit which is far enough
@@ -1517,7 +1505,7 @@ circuit_launch_by_extend_info(uint8_t purpose,
          * If we decide to probe the initial portion of these circs,
          * (up to the adversaries final hop), we need to remove this.
          */
-        circ->path_state = PATH_STATE_USE_SUCCEEDED;
+
         /* This must be called before the purpose change */
         pathbias_check_close(circ, END_CIRC_REASON_FINISHED);
       }