CDAT Migration Phase 3: Refactor utility functions and legacy code

[tomvothecoder]

Once all sets have been refactored, we should refactor the the following functions and code:

TBD once #677 is merged. Look for all TODO statements and add to the list below.

Todo:

• general.regrid_to_lower_res()
• hybrid_to_plevs() -- convert Z axis to mb units if in Pa
• Move all plots/cartopy files into root /plot file
• Implement e3sm_diags.driver.utils.regrid_subset_on_arm_coords(), which is the refactored version of e3sm_diags.utils.general.select_point.

Additional:

• [Bug]: Regridding time-series variable's climatology from hybrid to pressure levels breaks due to misaligned axes #721
• Replace climatology implementation to use xCDAT #726

[tomvothecoder]

This issue is no longer required because utility functions are refactored as we refactor the sets that use them.