Refactor and cleanup of HB PBL scheme

[jimmielin]

Originator(s): @mwaxmonsky (very lightly edited by @jimmielin)

Description (include issue title and the keyword ['closes', 'fixes', 'resolves'] and issue number):

• refactor and cleanup of Holtslag-Boville PBL scheme.

List all namelist files that were added or changed: N/A

List all files eliminated and why: N/A

List all files added and what they do: N/A

List all existing files that have been modified, and describe the changes:
(Helpful git command: git diff --name-status development...<your_branch_name>)

M       phys_utils/atmos_phys_pbl_utils.F90
  - moved minimum kvf limiter to HB logic instead of in common PBL utils code.

M       schemes/holtslag_boville/holtslag_boville_diff.F90
  - various refactoring and cleanup of HB PBL scheme into pure elemental functions.

List all automated tests that failed, as well as an explanation for why they weren't fixed: None (B4B)

Is this an answer-changing PR? If so, is it a new physics package, algorithm change, tuning change, etc?
B4B as tested in CAM against 64_137

If yes to the above question, describe how this code was validated with the new/modified features: