Drop the 'reordering' of longitude values.

[jbusecke]

I got quite frustrated with the attempt to make the step that reorders datasets along the longitude in #85, and will close that attempt.

I would like to advocate to drop this part of the preprocessing altogether.

My personal workflow has had numerous problems introduced by the attempt to 'reorder' the grid. In the end this is not necessary for many tasks, or it can be done at a later stage (e.g. when very intense processing is completed and you want to plot a map).

I also have the suspicion that recent changes introduced in #79 might cause #93, but I haven't confirmed this yet.
I am quite convinced we should drop the line ds = replace_x_y_nominal_lat_lon(ds) from combined_preprocessing.

Does anyone here crucially depend on that functionality?

My plan, for now, would be to remove it from the combined_preprocessing wrapper, but leave it in the module, so that users can apply it manually.

cc @dcherian @sckw @jetesdal @aaronspring

[jbusecke]

Closed via #104