Delete speaker users

[cjyabraham]

To improve security of the site, delete all "Speaker" users. Do it via a db call in the back-end so as not to trigger a ton of notification emails that will confuse speakers.

[cjyabraham]

I have deleted all speakers and all subscribers with no posts attributed to them. I've also deleted a few editors who had no content attributed. To stop emails going out, I told WP Mail SMTP to stop sending emails here. Here is the final set of users:

[cjyabraham]

I've also changed the admin username on the CNCF site, LFEvents and LFAsia.