[LAZY][VOTE] shut down diversity@a.o in favour of dev@diversity.a.o

[sebb]

I propose that the diversity@a.o list is shut down, and emails to the
list are bounced with a message to contact the dev@diversity.a.o list.

Unless there are any objections, I intend to raise the relevant INFRA
JIRA sometime after Fri 24th Sep 14:30 UTC.

Sebb.