Strip blank release notes when present

We're all a little tired of these slipping through despite the warnings.
This lint now automatically strips blank release notes and outputs a
warning.

Change-Id: Id0528a803e5b6c0713700ee84de20fd872854efd
Reviewed-on: https://gerrit.causes.com/23270
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Reviewed-by: Elliot Block <elliot.block@causes.com>