I'm not sure. Pros:

* Could speed up/help unwrapping of degenerate 3D images of shape (N, M, 1)

Cons:

* We can pass a shape (N, 1) array to do 1D phase unwrapping as the code is now (but I suppose we could find another way to make that work)
* What to do with a length 3 `wrap_aound` sequence if the squeeze changes the dimensionality?
* For a shape (N, M, 1, 3) 3D color image, the code raises an exception, as it is now, and that's good.

I think I'm against squeeze. If you want, we could raise a warning if one or more of the dimensions are zero?