CSS's admin loaders only add, and the per-admin cleanup in CreateAdminsJsonFile
reset AdminCache once per admin, so it only ever tracked the last one and a
reload never took anyone else out of memory. ReloadAdmins now removes every
admin it loaded last time and loads the new set in one tick. admins.json is
keyed by SteamID instead of name, so admins sharing a name aren't merged, and a
failed admins query keeps the loaded admins instead of removing them.