Punt loading many variables when only running accounts tasks.

Punt loading many variables when only running accounts tasks.

The All role has no such tasks.  The Front role just needs ~usernames~
and ~members~.  The Core role just needs these as well, except that
generating/checking fetchmail configs requires ~front_wg_addr~ and
~domain_name~.  The Gate role just updates/checks Gate's WireGuard™
config file, and the Campus role has /no/ accounts tasks: 1 tagged
task, 0 variables used.