* Remove 1 Google Log req and update required SCTs

For certificates issued on-or-after 15 April 2022, the Chrome CT Policy
will:
 - Remove the requirement that at least 1 SCT comes from a Google Log
 - Add a requirement that SCTs come from at least 2 log operators
 - Require 2 SCTs from distinct logs for certs with validities <= 180 days
 - Require 3 SCTs from distinct logs for certs with validities > 180
   days

Additional clarification was added to CT Enforcement Timeout section to
discuss Component Updater -delivered log lists.

* Clarify Log Operator Diversity

Added language describing how Chrome determines log operator diversity
in the event that a log changes operators.

Co-authored-by: devonobrien <asymmetric@chromium.org>