unmask dxt, dxu, dyt, dyu, dxtn, dyte output

[aekiss]

closes https://github.com/mom-ocean/MOM5/issues/375

[russfiedler]

@aekiss I've had a think about this and I don't think I can endorse this as it stands. It's a change specifically introduced for the benefit of a particular piece of post processing software and you would have to prove that it's not going to break somebody else's software that relies on the current version. Its' a bad habit to get into. I suggest making it a conditional compile for ACCESS or ACCESS-OM only.

[aekiss]

OK that's fair enough, I wasn't thinking of the bigger picture. It's hard to imagine anybody needing land masking in these grid fields, but I take your point. I won't bother with conditional compilation - people can use this branch from my fork if they ever need this.