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.