CF utilities consolidation

[daltonkell]

There are two modules proclaiming to be utilities for the CF specification checks:

• cf/util.py
• cfutil.py

Both contain functionality to help with CF checks. They should be consolidated into one module. I propose consolidation into cf/util.py.

[benjwadams]

While I agree this was a confusing decision, if I recall correctly a number of plugins may rely on modules being located in certain places. Changing the location of functions may break functionality for those existing checkers as was the case here: ioos/cc-plugin-glider#39

[daltonkell]

Perhaps we could scope out what might need to be done for these plugins to align everything