remove release note from next/

This is already in the 0.18 release notes but I missed deleting the file
from next/ because it was merged after I started drafting the notes.

Change-Id: I9e6898161f75524da78884cd872ff079a9e6bfe0
docs: s/e-mail/email/

I have always preferred the spelling "e-mail" but apparently I am living
in the past... IBM says, use "email".

Change-Id: I9b6d283eefcffe63a8861478b6fe5f1e15d387c2