Remove tracking timestamps for incoming network activity.

   Once 'cbtmincircs' build times are recorded, Tor clients update the

   distribution parameters and recompute the timeout every circuit completion

   (though see section 2.4.5 for when to pause and reset timeout due to

   network change or connectivity loss).

   too many circuits timing out).

   Tor clients calculate the parameters for a Pareto distribution fitting the

   data using the maximum likelihood estimator. For derivation, see:

   Tor clients attempt to detect both network connectivity loss and drastic

   changes in the timeout characteristics.

   Clients assume that they have had network connectivity loss if a circuit

   times out and have received no cells or TLS handshakes since that

   circuit began. Clients then temporarily stop counting timeouts until

   network activity resumes (ie: until a TLS handshake completes or a cell

   arrives at the client).

   To detect changing network conditions, clients keep a history of

   the timeout or non-timeout status of the past 'cbtrecentcount' circuits

   (20 circuits) that successfully completed at least one hop. If more than

   resets the timeout to 'cbtinitialtimeout' (60 seconds), and then begins

   recomputing the timeout.

   If the timeout was already 60 or higher, the client doubles the timeout.

   If the timeout was already at least `cbtinitialtimeout`,

   the client doubles the timeout.

2.4.6. Consensus parameters governing behavior