Removes all sensitive settings (passwords, auth tokens, urls, etc...) for
watcher notifications accounts. These settings were deprecated (and
herein removed) in favor of their secure sibling that is set inside the
elasticsearch keystore. For example:
`xpack.notification.email.account.<id>.smtp.password`
is no longer a valid setting, and it is replaced by
`xpack.notification.email.account.<id>.smtp.secure_password`
5308746270