[OpenPower-Firmware] Deleting master-next branch

[Stewart Smith]

Hi all,

As per my recent mail on process changes:

> Ignore the master-next branch. Pull requests and active
> development happens on the master branch. Releases are made out of the
> 'release' branch. The master-next branch will continue to exist for the
> 1.16 cycle so that any automated scripts can catch up.

We seem to be at the point where removing the master-next branch is the
thing to do. If you object, object now or forever hold your peace.

(i'll otherwise remove the master-next branch by end of the week, and
merge an update to our CONTRIBUTING.md:
https://github.com/open-power/op-build/pull/987 )

-- 
Stewart Smith
OPAL Architect, IBM.