Remove ERA-5 fliplat command and assert checks in base_grid.py to sup…

[rmholmes]

…port latitude reverse ordering in ERA-5.

Should I do something better than just removing the checks?

[micaeljtoliveira]

@aekiss You probably know what this is about, as you actively participated in the discussion of #4. Should we merge this as is?

[anton-seaice]

I think we should move the assert statements to a test, and test based on the grid type.

I.e. for most grids. " # The bottom latitude band should always be Southern extent." is a true statement but for ERA5, the opposite is true.

Saying that, many grids don't need these corner points, so the code is not actually relevant for ERA5 grids? I don't understand enough about the remapping in OM2 to know.