No longer use lastLoginTime

• strips all usage of lastLoginTime, which means:
  • no longer delete suspended users who have "Never Logged In" (as we couldn't be sure they hadn't)
  • no longer use "Logged in in last 24 months" as unnecessary/additional check for those to be deleted (just use lookup's cancelled date)
  • get cancelled date of all suspended users, i.e. including those who have potentially logged in in the last month (probably not many more)
• clean up some logging, primarily calc and log the number of people who would be deleted even if the delete_users option wasn't passed

Closes: https://gitlab.developers.cam.ac.uk/uis/devops/gsuite/operational-documentation/-/issues/111